Rain Water Harvesting

The Potential

The total amount of water that is received in the form of rainfall over an area is called the rainwater endowment of that area. Out of this, the amount that can be effectively harvested is called the water harvesting potential.Influencing factors Among the several factors that influence the rainwater harvesting potential of a site, eco-climatic conditions and the catchment characteristics are considered to be the most important.

a. Rainfall

i)Quantity: Rainfall is the most unpredictable variable in the calculation and hence, to determine the potential rainwater supply for a given catchment, reliable rainfall data are required, preferably for a period of at least10 years. Also, it would be far better to use rainfall data from the nearest station with comparable conditions.ii) Pattern: The number of annual rainy days also influences the need and design for rainwater harvesting. The fewer the annual rainy days or longer the dry period, the more the need for rainwater collection in a region. However, if the dry period is too long, big storage tanks would be needed to store rainwater. Hence in such regions, it is more feasible to use rainwater to recharge groundwater aquifers rather than for storage.b. Catchment area characteristics Runoff depends upon the area and type of the catchment over which it falls as well as surface features. All calculations relating to the performance of rainwater catchment systems involve the use of runoff coefficient to account for losses due to spillage, leakage, infiltration, catchment surface wetting and evaporation, which will all contribute to reducing the amount of runoff. (Runoff coefficient for any catchment is the ratio of the volume of water that runs off a surface to the volume of rainfall that falls on the surface).

Runoff coefficients for various catchment surfaces:

Type of Catchment

Coefficients

Roof Catchments - Tiles- Corrugated metal sheets

0.8- 0.90.7- 0.9

Ground surface coverings- Concrete- Brick pavement

0.6- 0.80.5- 0.6

Untreated ground catchments - Soil on slopes less than 10 per cent- Rocky natural catchments

0.0 - 0.30.2 - 0.5

Untreated ground catchments- Soil on slopes less than 10 per cent- Rocky natural catchments

1.0 - 0.30.2 - 0.5

Source : Pacey, Arnold and Cullis, Adrian 1989, Rainwater Harvesting: The collection of rainfall and runoff in rural areas, Intermediate Technology Publications, London

Based on the above factors the water harvesting potential of a site could be estimated using the formula given below.

Water harvesting potential = Rainfall (mm) x Area of catchment x Runoff coefficient

Harvesting SystemBroadly rainwater can be harvested for two purposes

Storing rainwater for ready use in containers above or below ground

Charged into the soil for withdrawal later (groundwater recharging)

Source: A Water Harvesting Manual For Urban Areas

From where to harvest rainRainwater harvesting can be harvested from the following surfaces

Rooftops: If buildings with impervious roofs are already in place, the catchment area is effectively available free of charge and they provide a supply at the point of consumption.

Paved and unpaved areas i.e., landscapes, open fields, parks, stormwater drains, roads and pavements and other open areas can be effectively used to harvest the runoff. The main advantage in using ground as collecting surface is that water can be collected from a larger area. This is particularly advantageous in areas of low rainfall.

Waterbodies: The potential of lakes, tanks and ponds to store rainwater is immense. The harvested rainwater can not only be used to meet water requirements of the city, it also recharges groundwater aquifers.

Stormwater drains: Most of the residential colonies have proper network of stormwater drains. If maintained neatly, these offer a simple and cost effective means for harvesting rainwater.

Whether to store rainwater or use it for recharge: The decision whether to store or recharge water depends on the rainfall pattern and the potential to do so, in a particular region. The sub-surface geology also plays an important role in making this decision.

For example, Delhi, Rajasthan and Gujarat where the total annual rainfall occurs during 3 or 4 months, are examples of places where groundwater recharge is usually practiced. In places like Kerala, Mizoram, Tamil Nadu and Bangalore where rain falls throughout the year barring a few dry periods, one can depend on a small sized tank for storing rainwater, since the period between two spells of rain is short. Wherever sub-strata is impermeable recharging will not be feasible. Hence, it would be ideal to opt for storage.

In places where the groundwater is saline or not of potable standards, the alternate system could be that of storing rainwater.

Beyond generalisations, it is the requirement that governs the choice of water harvesting technique. For example, in Ahemadabad, which has limited number of rainy days as that of Delhi, traditional rainwater harvesting tanks, known as tankas, are used to store rainwater even today in residential areas, temples and hotels.

Source: A water harvesting manualfor urban areas

COMPONENTS OF A RAINWATER HARVESTING SYSTEM A rainwater harvesting system comprises components of various stages - transporting rainwater through pipes or drains, filtration, and storage in tanks for reuse or recharge. The common components of a rainwater harvesting system involved in these stages are illustrated here. 1. Catchments: The catchment of a water harvesting system is the surface which directly receives the rainfall and provides water to the system. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or open ground. A roof made of reinforced cement concrete (RCC), galvanised iron or corrugated sheets can also be used for water harvesting.

Source: A water harvesting manual for urban areas

2. Coarse mesh at the roof to prevent the passage of debris3. Gutters: Channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank. Gutters can be semi-circular or rectangular and could be made using:

Locally available material such as plain galvanised iron sheet (20 to 22 gauge), folded to required shapes.

Semi-circular gutters of PVC material can be readily prepared by cutting those pipes into two equal semi-circular channels.

Bamboo or betel trunks cut vertically in half.

The size of the gutter should be according to the flow during the highest intensity rain. It is advisable to make them 10 to 15 per cent oversize.

Gutters need to be supported so they do not sag or fall off when loaded with water. The way in which gutters are fixed depends on the construction of the house; it is possible to fix iron or timber brackets into the walls, but for houses having wider eaves, some method of attachment to the rafters is necessary.

ConduitsConduits are pipelines or drains that carry rainwater from the catchment or rooftop area to the harvesting system. Conduits can be of any material like polyvinyl chloride (PVC) or galvanized iron (GI), materials that are commonly available.

The following table gives an idea about the diameter of pipe required for draining out rainwater based on rainfall intensity and roof area:

Sizing of rainwater pipe for roof drainage

Diameter Of pipe (mm)

Average rate of rainfall in mm/h

50

75

100

125

150

200

50

13.4

8.9

6.6

5.3

4.4

3.3

65

24.1

16.0

12.0

9.6

8.0

6.0

75

40.8

27.0

20.4

16.3

13.6

10.2

100

85.4

57.0

42.7

34.2

28.5

21.3

125

-

-

80.5

64.3

53.5

40.0

150

-

-

-

-

83.6

62.7

mm/ h - millimeters per hour; m - meters Source: National Building Code

5. First-flushing A first flush device is a valve that ensures that runoff from the first spell of rain is flushed out and does not enter the system. This needs to be done since the first spell of rain carries a relatively larger amount of pollutants from the air and catchment surface.

Source: A water harvesting manual for urban areas

6. Filter The filter is used to remove suspended pollutants from rainwater collected over roof. A filter unit is a chamber filled with filtering media such as fibre, coarse sand and gravel layers to remove debris and dirt from water before it enters the storage tank or recharge structure. Charcoal can be added for additional filtration.

Source: A water harvesting manualfor urban areas

(i) Charcoal water filterA simple charcoal filter can be made in a drum or an earthen pot. The filter is made of gravel, sand and charcoal, all of which are easily available.

(ii) Sand filtersSand filters have commonly available sand as filter media. Sand filters are easy and inexpensive to construct. These filters can be employed for treatment of water to effectively remove turbidity (suspended particles like silt and clay), colour and microorganisms.

Source: A water harvesting manual for urban areas

In a simple sand filter that can be constructed domestically, the top layer comprises coarse sand followed by a 5-10 mm layer of gravel followed by another 5-25 cm layer of gravel and boulders.

(ii. a) Dewas filtersMost residents in Dewas, Madhya Pradesh, have wells in their houses. Formerly, all that those wells would do was extract groundwater. But then, the district administration of Dewas initiated a groundwater recharge scheme. The rooftop water was collected and allowed to pass through a filter system called the Dewas fillter, designed by Mohan Rao , district collecter of Dewas, and engineers of the rural engineering services. The water thus filtered is put into the service tubewell.

The filter consists of a polyvinyl chloride (PVC) pipe 140 mm in diameter and 1.2m long. There are three chambers. The first purification chamber has pebbles varying between 2-6 mm, the second chamber has slightly larger pebbles, between 6 and 12 mm and the third chamber has the largest - 12-20 mm pebbles. There is a mesh at the outflow side through which clean water flows out after passing through the three chambers. The cost of this filter unit is Rs 600.

Filter for large rooftops:When rainwater is harvested in a large rooftop area, the filtering system should accommodate the excess flow. A system is designed with three concentric circular chambers in which the outer chamber is filled with sand, the middle one with coarse aggregate and the inner-most layer with pebbles.

This way the area of filtration is increased for sand, in relation to coarse aggregate and pebbles. Rainwater reaches the centre core and is collected in the sump where it is treated with few tablets of chlorine and is made ready for consumption. This system was designed byR Jeyakumar(Source: Jeyakumar; Rain water Harvest Manual P-21)

Varun:S Vishwanath, a Bangalore water harvesting expert, has developed a rainwater filter "VARUN". According to him, from a decently clean roof 'VARUN' can handle a 50 mm per hour intensity rainfall from a 50 square metre roof area. This means the product is relatively standardised. For new house builders we therefore can recommend the number of downpipes they have to optimise on and the number of filters they will need.

'VARUN' is made from a 90 litre High Density Poly Ethylene (HDPE) drum. The lid is turned over and holes are puched in it. This is the first sieve which keeps out large leaves, twigs etc. Rainwater coming out of the lid sieve then passes through three layers of sponge and a 150 mm thick layer of coarse sand. Presence of sponge makes the cleaning process very easy. Remove the first layer of sponge and soak /clean it in a bucket of water (which you then don't waste but use it for plants). The sand needs no cleaning at all. The basic cost of the filter is about Rs 2250/-

ii. b. Horizontal roughing filter and slow sand filterThe introducton of horizontal roughing filter and slow sand filter (HRF/SSF) to treat surface water has made safe drinking water available in coastal pockets of Orissa. The major components of this filter are described below.1) Filter channel : One square metre in cross-section and eight m in length, laid across the tank embankment, the filter channel consists of three uniform compartments, the first packed with broken bricks, the second with coarse sand, followed by fine sand in the third compartment. The HRF usually consists of filter material like gravel and coarse sand that successively decreases in size from 25 mm to 4 mm. The bulk of solids in the incoming water is separated by this coarse filter media or HRF. At every outlet and inlet point of the channel, fine graded mesh is implanted to prevent entry of finer materials into the sump. The length of a channel varies according to the nature of the site selected for the sump.

2) Sump: A storage provision to collect filtered water from the tank through the filter channel for storage and collection. While HRF acts as a physical filter and is applied to retain solid matter, SSF is primarily a biological filter, used to kill microbes in the water. Both filter types are generally stable, making full use of the natural purification process of harvested surface water and do not require any chemicals. For more details: Making Water Everybody's Business

iii. Rain PC AcquaSure, a consortium of three specialist Netherlands-based companies, has developed a system for the conversion of rainwater to drinking water in the form of a Rainwater Purification Centre (RainPC).

RainPC is developed by scaling down the multi-staged water treatment method (MST), which involves screening, flocculation sedimentation and filtration and incorporating existing technologies like upward flow fine filtration, absorption and ion exchange. Coming in a small compact 26 kg unit, the RainPC offers an affordable solution by converting rainwater into drinking water.

RainPC is made of ultra violet resistant poly-ethylene housing and cover, stainless steel rods and bolts, a nickel-brass valve and an adapter for maintaining constant volume. Xenotex-A and activated carbon catridges along with ultra membrane filtration or micro-membrane filtration modules incorporated in the RainPC has the capacity to deal with E-coli and the potential of meeting the Dutch as well as World Health Organisations (WHO) water regulation standards. The components can also be transported individually to be assembled at the site. Three product types are available based on their microbial contaminant removal capacity. This technology is ideally suited for virtually any situation and is a blessing particularly for those who have little or no access to regular safe drinking water.

The salient features of Rain PC are:

Simple straight-forward installation

Easy to operate and maintain

Needs no power and operates at low gravity pressure (0.1 bar upward).

The system is capable of providing a constant flow of about 40 liters of rainwater per hour, enough for a family of five for drinking, cooking and bathing purposes.

Maintains nearly constant volume irrespective of water pressure.

The Xenotex-A and activated carbon cartridge processes up to 20,000 liters and can be regenerated up to 10 times.

Cost per 1000 litres is as low as US$ 2 to 3.

(The above information is as per the manufacturers' claims and not based on any study by CSE.) For further information Email: cleanwater@aquasure.nl

iv. Rainwater harvester EA Water Pvt Ltd has launched a unique Rainwater Harvester, which filters runoff water from roads, which generally contains oil and grease. This system has been installed in the Gymkhana club, Sector-15, Faridabad, Haryana. Rajit Malohtra, project in charge, of this company explained that the water harvesting system installed at the club has a sand filter, which filters silt from runoff harvested from roof, lawns and parking area. The cost of the filter is around Rs 60,000.For more details, contact EA Water PVT Limited,504 empire apartments,Mehrauli-Gurgaon Road,SultanpurNew Delhi-110 030Phone: 011-2680062Website: www.eawater.com

Filters available in the German Market According to Wessels (1994), concerns over the possible negative health effects of rainwater utilisation led to some opposition. The Federal Office of Health, for example, intially objected to its use for washing clothes, personal hygiene and even for toilet flushing, due to possible risks of infection and allergic reactions. Long-term investigations by the health offices in Hamburg and Bremen, however, have yielded positive results with respect to the use of water for washing purposes and have confirmed that rainwater sources do not present a health risk.

(i) Filters developed by WISYPrivate companies such as WISY, based in Kefenrod in Germany, are playing an important role in promoting rainwater use by developing pumps and filter devices to improve water quality. WISY has developed a simple filter system, which can be attached to a standard household downpipe. Under conditions in Germany (assuming a mean annual rainfall of 650mm/year), this can divert and filter 90 per cent of the runoff from a roof area of up to 200 square metre.

(a)

(fig a). A filter collector diverts 90 per cent of rainwater to a storage tank through a 0.17 mm stainless steel mesh filter.

(b)

(fig b). A larger vortex fine filter can cope with run-off from roof areas of up to 500 square metre.

(c)

(fig c). A floating fine suction filter for ensuring that the water pumped from the tank is extracted from the cleanest part of the tank and is free of particulates has also been developed.For details contact: WISY (Winkler system)OT Hitzkirchen, Oberdorfstrasse 26,D-63699, Kefendrod-HitzkirchenGermany; fax:+60-54-912129Wisyag@t-online.de(Source: John Gould and Erik Nissen-Petersen, 1999: Rainwater Catchment Systems for Domestic Supply - Design, Construction and Implementation, Intermediate Technology Group)

(ii) Filters developed by MALLBETON Another company, MALLBETON, a manufacturer of concrete tanks and filters, based in Germany, is marketing a tank design which manages any overflows (Konig, 1998). This is done by constructing the top half of a sub-surface tank from a porous concrete ring, which allows water to gradually seep into the ground. While this reduces the volume of water available, it does make householders eligible for waivers on their rainwater drainage fees. These fees are already applied to householders and businesses in about 25 per cent of Germany. The charges that are levied on each square metre of roof area and sealed surroundings can be substantial, such as in Bonn, so waivers often provide significant savings.(Source: John Gould and Erik Nissen-Petersen, 1999: Rainwater Catchment Systems for Domestic Supply - Design, Construction and Implementation, Intermediate Technology Group)

A storage tank made of galvanised iron sheets

Storage facilityThere are various options available for the construction of these tanks with respect to the shape, size and the material of construction. Shape: Cylindrical, rectangular and square. Material of construction: Reinforced cement concrete, (RCC), ferrocement, masonry, plastic (polyethylene) or metal (galvanised iron) sheets are commonly used.Position of tank: Depending on space availability these tanks could be constructed above ground, partly underground or fully underground. Some maintenance measures like cleaning and disinfection are required to ensure the quality of water stored in the container.

8. Recharge structures Rainwater may be charged into the groundwater aquifers through any suitable structures like dugwells, borewells, recharge trenches and recharge pits. Various recharge structures are possible - some which promote the percolation of water through soil strata at shallower depth (e.g., recharge trenches, permeable pavements) whereas others conduct water to greater depths from where it joins the groundwater (e.g. recharge wells). At many locations, existing structures like wells, pits and tanks can be modified as recharge structures, eliminating the need to construct any structures afresh. Here are a few commonly used recharging methods:

1. Recharging of dugwells and abandoned tubewells. In alluvial and hard rock areas, there are thousands of wells which have either gone dry or whose water levels have declined considerably. These can be recharged directly with rooftop run-off. Rainwater that is collected on the rooftop of the building is diverted by drainpipes to a settlement or filtration tank, from which it flows into the recharge well (borewell or dugwell).

If a tubewell is used for recharging, then the casing (outer pipe) should preferably be a slotted or perforated pipe so that more surface area is available for the water to percolate. Developing a borewell would increase its recharging capacity (developing is the process where water or air is forced into the well under pressure to loosen the soil strata surrounding the bore to make it more permeable).

If a dugwell is used for recharge, the well lining should have openings (weep-holes) at regular intervals to allow seepage of water through the sides. Dugwells should be covered to prevent mosquito breeding and entry of leaves and debris. The bottom of recharge wells should be desilted annually to maintain the intake capacity.

Providing the following elements in the system can ensure the quality of water entering the recharge wells:1. Filter mesh at entrance point of rooftop drains 2. Settlement chamber3. Filter bed

A settlement chamber

2. Settlement tankSettlement tanks are used to remove silt and other floating impurities from rainwater. A settlement tank is like an ordinary storage container having provisions for inflow (bringing water from the catchment), outflow (carrying water to the recharge well) and overflow. A settlement tank can have an unpaved bottom surface to allow standing water to percolate into the soil.

In case of excess rainfall, the rate of recharge, especially of borewells, may not match the rate of rainfall. In such situations, the desilting chamber holds the excess amount of water till it is soaked up by the recharge structure. Thus, the settlement chamber acts like a buffer in the system.

Any container, (masonry or concrete underground tanks, old unused tanks, pre-fabricated PVC or ferrocement tanks) with adequate capacity of storage can be used as a settlement tank.

3. Recharging of service tubewells. In this case the rooftop runoff is not directly led into the service tubewells, to avoid chances of contamination of groundwater. Instead rainwater is collected in a recharge well, which is a temporary storage tank (located near the service tubewell), with a borehole, which is shallower than the water table. This borehole has to be provided with a casing pipe to prevent the caving in of soil, if the strata is loose. A filter chamber comprising of sand, gravel and boulders is provided to arrest the impurities.

4. Recharge pits A recharge pit is 1.5m to 3m wide and 2m to 3m deep. The excavated pit is lined with a brick/stone wall with openings (weep-holes) at regular intervals. The top area of the pit can be covered with a perforated cover. Design procedure is the same as that of a settlement tank.

5. Soakaways / Percolation pit

Filter materials in a soakaway

Percolation pits, one of the easiest and most effective means of harvesting rainwater, are generally not more than 60 x 60 x 60 cm pits, (designed on the basis of expected runoff as described for settlement tanks), filled with pebbles or brick jelly and river sand, covered with perforated concrete slabs wherever necessary.

6.Recharge trenches A recharge trench is a continuous trench excavated in the ground and refilled with porous media like pebbles, boulders or broken bricks. A recharge trench can be 0.5 m to 1 m wide and 1 m to 1.5 m deep. The length of the recharge trench is decided as per the amount of runoff expected. The recharge trench should be periodically cleaned of accumulated debris to maintain the intake capacity. In terms of recharge rates, recharge trenches are relatively less effective since the soil strata at depth of about 1.5 metres is generally less permeable. For recharging through recharge trenches, fewer precautions have to be taken to maintain the quality of the rainfall runoff. Runoff from both paved and unpaved catchments can be tapped.

7.Recharge troughs

Source: A water harvesting manual for urban areas

To collect the runoff from paved or unpaved areas draining out of a compound, recharge troughs are commonly placed at the entrance of a residential/institutional complex.These structures are similar to recharge trenches except for the fact that the excavated portion is not filled with filter materials. In order to facilitate speedy recharge, boreholes are drilled at regular intervals in this trench. In design part, there is no need of incorporating the influence of filter materials.This structure is capable of harvesting only a limited amount of runoff because of the limitation with regard to size.

8. Modified injection well In this method water is not pumped into the aquifer but allowed to percolate through a filter bed, which comprises sand and gravel. A modified injection well is generally a borehole, 500 mm diameter, which is drilled to the desired depth depending upon the geological conditions, preferably 2 to 3 m below the water table in the area. Inside this hole a slotted casing pipe of 200 mm diameter is inserted. The annular space between the borehole and the pipe is filled with gravel and developed with a compressor till it gives clear water. To stop the suspended solids from entering the recharge tubewell, a filter mechanism is provided at the top.

Do you want your rainwater harvesting system to crack and collapse; leak and flood the surrounding areas? If not, then ensure that the design is proper.Effectiveness of the rainwater harvesting depends on appropriate design of the systems. Be it storage or a recharge structure, an improperly designed system will lead to operational problems, thereby raising the operation and maintenance costs. It may even lead to the abandoning of the structure put in place. A few design tips to put the right water harvesting system at the right place.

Design of a rainwater harvesting storage tankDesign of a recharge structures

Design of storage tanksThe volume of the storage tank can be determined by the following factors:

Number of persons in the household: The greater the number of persons, the greater the storage capacity required to achieve the same efficiency of fewer people under the same roof area.

Per capita water requirement: This varies from household to household based on habits and also from season to season. Consumption rate has an impact on the storage systems design as well as the duration to which stored rainwater can last.

Average annual rainfall

Period of water scarcity: Apart from the total rainfall, the pattern of rainfall -whether evenly distributed through the year or concentrated in certain periods will determine the storage requirement. The more distributed the pattern, the lesser the size.

Type and size of the catchment:Type of roofing material determines the selection of the runoff coefficient for designs. Size could be assessed by measuring the area covered by the catchment i.e., the length and horizontal width. Larger the catchment, larger the size of the required cistern (tank).

Dry season demand versus supply approachIn this approach there are three options for determining the volume of storage:

1. Matching the capacity of the tank to the area of the roof

2. Matching the capacity of the tank to the quantity of water required by its users

3. Choosing a tank size that is appropriate in terms of costs, resources and construction methods.

In practice the costs, resources and the construction methods tend to limit the tanks to smaller capacities than would otherwise be justified by roof areas or likely needs of consumers. For this reason elaborate calculations aimed at matching tank capacity to roof area is usually unnecessary. However a simplified calculation based on the following factors can give a rough idea of the potential for rainwater colection.

Illustration Suppose the system has to be designed for meeting drinking water requirement of a five-member family living in a building with a rooftop area of 100 sq. m. The average annual rainfall in the region is 600 mm (average annual rainfall in Delhi is 611 mm). Daily drinking water requirement per person (drinking and cooking) is 10 litres.

Design procedure:Following details are available:Area of the catchment (A) = 100 sq. m.Average annual rainfall (R) = 611 mm (0.61 m)Runoff coefficient (C) = 0.85 1. Calculate the maximum amount of rainfall that can be harvested from the rooftop:Annual water harvesting potential = 100 x 0.6 x 0.85= 51 cu. m. (51,000 litres)2. Determine the tank capacity: This is based on the dry period, i.e., the period between the two consecutive rainy seasons. For example, with a monsoon extending over four months, the dry season is of 245 days.3. Calculate drinking water requirement for the family for the dry season = 245 x 5 x 10= 12,250 litres

As a safety factor, the tank should be built 20 per cent larger than required, i.e., 14,700 litres. This tank can meet the basic drinking water requirement of a 5-member family for the dry period. A typical size of a rectangular tank constructed in the basement will be about 4.0 m x 4.0 m x 1.0 m

Salient features of this approach:

1. Simplest approach to system design but is relevant only in areas where distinct dry seasons exist

2. Provides a rough estimate of storage volume requirements

3. This method does not take into account variations between different years, such as the occurrence of drought years. It also entirely ignores rainfall input and the capacity of the catchment to deliver the runoff necessary to fill the storage tank.

4. This technique can be used in the absence of any rainfall data and is easily understandable to the layperson.These points are especially relevant when designing systems in the remote areas of developing countries where obtaining reliable rainfall data can be difficult.

Design of groundwater recharge structuresRecharge of aquifers In places where the withdrawal of water is more than the rate of recharge an imbalance in the groundwater reserves is created. Recharging of aquifers are undertaken with the following objectives:

To maintain or augment natural groundwater as an economic resource

To conserve excess surface water underground

To combat progressive depletion of groundwater levels

To combat unfavourable salt balance and saline water intrusion

Design of an aquifer recharge system To achieve the objectives it is imperative to plan out an artificial recharge scheme in a scientific manner. Thus it is imperative that proper scientific investigations be carried out for selection of site for artificial recharge of groundwater. The proper design will include the following considerations:Selection of site: Recharge structures should be planned out after conducting proper hydro-geological investigations. Based on the analysis of this data (already existing or those collected during investigation) it should be possible to: Define the sub-surface geology. Determine the presence or absence of impermeable layers or lenses that can impede percolation Define depths to water table and groundwater flow directions Establish the maximum rate of recharge that could be achieved at the site.Source of water used for recharge: Basically the potential of rainwater harvesting and the quantity and quality of water available for recharging, have to be assessed.

3. Engineering, construction and costs

4. Operation, maintenance and monitoring

Design of recharge structures and settlement tank

For designing the optimum capacity of the tank, the following parameters need to be considered:

1.) Size of the catchment

2.) Intensity of rainfall

3.) Rate of recharge, which depends on the geology of the site

The capacity of the tank should be enough to retain the runoff occurring from conditions of peak rainfall intensity. The rate of recharge in comparison to runoff is a critical factor. However, since accurate recharge rates are not available without detailed geo-hydrological studies, the rates have to be assumed. The capacity of recharge tank is designed to retain runoff from at least 15 minutes rainfall of peak intensity. (For Delhi, peak hourly rainfall is 90 mm (based on 25 year frequency) and 15 minutes peak rainfall is 22.5 mm/hr, say, 25 mm, according to CGWB norms).

IllustrationFor an area of 100 sq. m.,volume of desilting tank required in Delhi = 100 x 0.025 x 0.85 = 2.125 cu. m. (2,125 litres)

Design of a recharge trenchThe methodology of design of a recharge trench is similar to that for a settlement tank. The difference is that the water-holding capacity of a recharge trench is less than its gross volume because it is filled with porous material. A factor of loose density of the media (void ratio) has to be applied to the equation. The void ratio of the filler material varies with the kind of material used, but for commonly used materials like brickbats, pebbles and gravel, a void ratio of 0.5 may be assumed.Using the same method as used for designing a settlement tank:Assuming a void ratio of 0.5, the required capacity of a recharge tank = (100 x 0.025 x 0.85)/0.5 = 4.25 cu. m. (4,250 litres)

In designing a recharge trench, the length of the trench is an important factor. Once the required capacity is calculated, length can be calculated by considering a fixed depth and width.

ConstructionProcedures and specifications for construction of storage and recharge tanks are explained below. There are a lot of similarities in the construction steps of both storage and recharge structures.

Construction of a masonry tank under progress

I. Masonry Tanks:

When building brick walls for water tanks, both horizontal and vertical joints are filled with mortar of a ration of 1:4. For obtaining maximum strength, lay out a circle of bricks or blocks on the foundation without mortar, with such spacing that no brick or block is cut to fit into the circle. A proper foundation of cement concrete will also have to be provided.

Each brick or block should be dipped in water to saturate and make it waterproof. Thereafter these bricks are laid upon the cement mortar.

Bricks and blocks in walls should be sprinkled with water just before plastering for bonding. The right way to apply plaster is to throw a thin coat of mortar (1:3) on to the inner wall and then a thin coat of 1:4 mortar on the outer wall while the first coat settles, and so on until the required thickness of plaster is reached. The surface of each coat of plaster, except the final one, is made rough to make sure there is good bonding between coats.

For simplicity and maximum strength, walls built of burnt bricks, or blocks made from compressed sandy soil and cement, rubble stones and concrete are reinforced after they have been built to their final height.

Plaster on the walls of water tanks must not be allowed to dry or be exposed to sunshine for the first three weeks. The process of keeping the mortar wet is called curing. Covering the walls with polythene sheeting or plastic sacks, which must be properly secured against the walls using the sisal strings, does this. Water is poured between the wall and the sacks or polythene morning and evening for three weeks. The external wall can be made weather proof (if the tank is above the ground level) with two coats made of 1 part cement to 10 parts lime.

II. Reinforced Cement Concrete Tank (RCC) Reinforced concrete tanks can be built above or below the ground. Concrete is durable and long-lasting, but is subject to cracking. An advantage of concrete cisterns is their ability to decrease the corrosiveness of rainwater by allowing the dissolution of calcium carbonate from the walls and floors. Each tank must have an overflow system for situations when excess water enters the tank. The overflow can be connected to the drainage system.

Design and construction of reinforced cement concrete tanks shall comply with the requirements of IS 3370 (part-I)-1965 and IS 456-1964. Accordingly the mix of cement concrete shall not be leaner than 1:2:4 ( 1 part cement: 2 parts of coarse sand and 4 parts of stone aggregates of 20 mm nominal size)

When constructing water tanks it is essential to adhere to a few basic yet critical rules with respect to correct mixtures and applications of concrete and mortar. These include:

Mixing cement, aggregate and water properly, and not adding too much water

Applying the mortar or concrete within a maximum of half an hour of mixing

Curing cement work properly by keeping it moist and under shade for at least three weeks after its application.

III. Ferro Cement Jars: Ferrocement consists of a thin sheet of cement mortar which is reinforced with a cage made of wire mesh and steel bars. Because ferrocement is structurally more effectient than masonry, the thickness of the walls of the container are as low as 10 to 15 mm. Ferrocement components can be casted in any shape using suitable moulds. The technology is extremely simple to implement, and even semi-skilled workpersons can learn it with ease. Ferrocement requires only a few easily available materials - cement, sand, galvanized iron (GI) wire mesh, and mild steel (MS) bars - in small amounts compared to masonry and RCC.a. Pot shaped container: The process of construction of a pot shaped ferro cement container is quite simple. The only materials required are hessian cloth, chaff (waste from agricultural produce), GI wire mesh, MS bars, cement and sand.

Preparation of mould: The hessian cloth is first stiched into a sack resembling the shape of a container. It is then filled with chaff that is compacted in layers. Dry leaves or dry grass can also be used in place of chaff. Once the sack is filled with the filler material, it is beaten into the required shape by a wooden bat.

Source: Catchwater

Laying of reinforcement: A GI wire mesh (22-26 guage - see table) is tied around the mould leaving sockets at suitable locations for inlet, over flow and cleaning pipes. Tying 6 mm diameter MS bars at wide intervals both horizontally and vertically strengthens the reinforcement cage.

Preparation of cement mortar for plastering: Cement mortar of suitable proportion (see table) is prepared, having water content equal to 0.45 times the volume of cement.

Capacity of containerLitres

Thickness of the walls

Ratio Cement: sand

Thickness of GI wire (guage)

400

10

1:3

26

600

10

1:3

24

900

12

1:2:5

24

1500

15

1:2:5

22

Plastering: The mortar is plastered in two layers along the wall thickness, the second layer being applied 24 hours after the first. The ferro cement wall normally has a thickness of 10 to 15 mm, depending on the volume of the container. The cement mortar is applied ensuring a minimum clearance (cover) 3 mm between the reinforcement mesh and the outer surfaces of the wall.

Removal of mould: The mould of the container is removed 24 hours after casting of the wall is completed, by removing the filler material. The container can be brought into use after 10 days of wet curing.

b. Ferrocement Tank using Skeletal Cage: Phases of constructioni Selection of siteii Marking for circular foundation:Choose the diameter of foundation (Df) for required storage capacity from the table

Capacity of storage tank (litres)

5,000 and 6,000

7,000 and 8,000

9,000 and 10,000

Df

2.40 m

2.70 m

3.00 m

iii Excavation for foundationiv Compacting the excavated pitv Placing cement concrete in foundation: Prepare Plain Cement Concrete of 1:4:8 mix ( 1 cement: 4 sand: 8 stone aggregate of 40mm size)vi Erection of mould/ Preparation of elements of skeletal cagevii a. Preparation of Elements of Skeletal Cage:

Source: Action for food Production and United Nations Children's Fund, Rooftop rainwater harvesting systems

Skeletal cage is an assembly of 4 types of elements (of different shapes) made from mild steel rods. They are

'U' shaped elements

'L' shaped elements

'' shaped elements

'O' shaped elements

Dimensions of elements for tank capacities 5,000 litres to 10,000 litres

Element

No.

Dimensions

Capacity of Storage Tank (in litres)

5,000

6,000

7,000

8,000

9,000

10,000

u

2

H

1.8

2.1

1.9

2.1

1.9

2.1

W1

2.05

2.05

2.35

2.35

2.65

2.65

4

H

1.8

2.1

1.9

2.1

1.9

2.1

L

W2

0.82

0.82

0.95

0.95

1.05

1.05

8

H

1.8

2.1

1.9

2.1

1.9

2.1

L

W3

0.5

0.5

0.6

0.6

0.65

0.65

D1

9Nos

11Nos

10Nos

11Nos

10Nos

11Nos

2.05

2.05

2.35

2.35

2.65

2.65

1

D2

1.25

1.25

1.41

1.41

1.60

1.60

1

D3

0.62

0.62

0.71

0.71

0.84

0.80

Source: Action for food Production and United Nations Children's Fund, Rooftop rainwater harvesting systems

Notes:* Refer to above table for dimensions and number of each of these elements for 5,000, 6,000, 7,000, 8,000, 9,000 and 10,000 litres capacity system* Use 6 mm diameter rods for preparing 'U', 'L' and '' shaped elements. Use 4 mm diameter GI wire for "O" shaped elements (Circular rings)* Straighten, cut and bend the mild steel rods to form these elements* Adopt an overlap length of 10 cm in forming the circular elements.

b. Assembling the elements:

Place the two 'U' shaped rods vertically over the foundation, perpendicular to each other

Place the outer, middle and inner rings over the two 'U' shaped rods, coinciding with the circular marking and tie the intersections with binding wires

Place and tie 4 'L' shaped elements on the center marking of each quarter, each rod extending upto the inner most ring

Place and tie 8 '' shaped elements on the remaining markings, each element extending to the middle ring

Place and tie all the rings of diameter 'D1" over the vertical reinforcement at a uniform spacing of 20 cm

For providing cylindrical shape to the skeletal cage, fix cross bars at the top of skeletal cage and ie with ropes, 3-4 vertical rods to wooden pegs pegged to the ground.

c. Tying of mesh over skeletal cage: Select the reinforcement mesh that suits the capacity of the tank from the table below:

Capacity of Tank (Lt)

5,000 & 6,000

7,000 & 8,000

9,000 & 10,000

Specification of wire mesh

Chicken wire mesh of 22 gauge and 12 mm (1/2") opening

Chicken wire mesh of 20 gauge and 25 mm (1") opening

Chicken wire mesh of 20 gauge and 25 mm (1") opening

Source: Action for food Production and United Nations Children's Fund, Rooftop rainwater harvesting systems

Note: Woven wire mesh of rectangular opening, of same specifications mentioned above, can be used if chicken wire mesh is not available Wrap two layers of selected mesh, one layer on the outer side and one layer on the inner side of the skeletal cage. Tie the mesh with binding wire to the skeletal cage at all intersections of elementsProvide a tucking length of 30 cm (1 foot) at the baseProject the mesh 10 cm above the top of the skeletal cage Cut the skeletal cage and insert pipe fixtures such as overflow pipe, drain pipe and tap at appropriate places as given in table

Over flow pipe

10 cm below the top of cage

Drain pipe

5 cm above the foundation

Tap

10 cm above the foundation

viii. Plastering the tank's outside wall

Prepare cement slurry (cement mixed with water) and add anti-rust agent (chrometrioxide tablets)

Apply one coat of cement slurry (mix of cement and water) over the mesh using a painting brush

Prepare cement mortar of depending on capacity of tank

Apply the first coat of cement mortar on the outer surface at a thickness of 1 cm. Care has to be taken to fill the space between the two layers completely. This could be done by using a GI sheet, slightly curved in shape to be held close to the skeletal cage from inside by a person, while cement mortar is applied by another from outside

Leave 10 cm of mesh projected above the cage unplastered in order to join the skeletal dome to the tank

After two hours, apply a second coat of mortar of a thickness of 1 cm.

ix. Plastering the tank's inside wall

After two hours of outside plastering, apply cement slurry to the inner surface of the tank wall

Prepare cement mortar of 1: 3 mix and add waterproof compound in liquid form

Apply first coat of cement mortar of 1 cm thickness on the inner surface, starting from bottom of the tank moving laterally and progressing towards the top

After two hours, apply second coat of mortar to attain a total wall thickness of 2 cm

Apply cement slurry as final coat on outer and inner surfaces of tank and smoothen using coir brush.

x. Removal of mouldxi. Casting of tank floor:

Sprinkle cement slurry over the foundation concrete

Prepare plain cement concrete of 1:2:4 mix ( 1 cement: 2 sand: 4 stone aggregate of 12 mm size), pour it over the base and compact to a thickness of 50 mm (2 inch)

Finish the floor base using cement mortar keeping the slope towards the drain pipe

Finish the wall and base joints (inner and outer) with cement mortar

Twelve hours after setting the tank floor, add waterproof compound (liquid form) with cement slurry and apply it over inside surface of the tank and smoothen with coir brush

xii. Curing the tank

Cure the tank for 14 days by pouring water thrice a day or covering the tank with wet gunny bags

In coastal areas, after curing for 14 days, apply rust proof paint over the outer surface of tank wall

xiii. Construction of roof for the tank

An assembly of mild steel elements is prepared as a skeletal frame for the roof. Chicken wire mesh is tied over it and plastered in cement mortar

The roof is provided with two openings. One is an opening of diameter 35 cm for accommodating the filter container. Another is a manhole with a 60 cm opening. The opening for the filter will be on one side of the roof. The manhole is provided at the centre of dome

Recharge wella) Construction of a new recharge well

Step 1: Excavating the earth

Step 2: Making a borehole to facilitate groundwater recharging

Step 3: Providing masonry or RCC walls in the excavated portion and thereafter providing the filter materials.

Step 4: Covering the tank made with a RCC or stone slab provided with a manhole.

b) Conversion of a dried up tube well into a recharge well

Step 1: Replace top few metres of the cast iron casing pipe of the dried tubewell with a perforated poly Vinyl chloride (PVC) pipe.

Step 2: Wrap the perforations with a screen-made of either coir screen or closely knit nylon mesh.

Quality of stored waterTo prevent leaves and debris from entering the system, mesh filters should be provided at the mouth of the drainpipe. Further, a first-flush device should be provided in the conduit before it connects to the storage container.If the stored water is to be used for drinking purposes, a sand filter should also be provided. Methods to protect rainwater quality include appropriate system design, sound operation and maintenance and use of first flush devices and treatment. Treatment is mainly appropriate as a remedial action if contamination is expected. First flush devices can be effective in reducing levels of contamination if properly maintained. Good system design, operation and maintenance are generally the simplest and most effective means of protecting water quality.

a. System design: The best initial step to protecting water quality is to ensure good system design. Water quality will generally improve during storage provided sunlight and living organisms are excluded from the tank and fresh inflows do not stir up any sediment. The design should include

Clean impervious made from smooth, clean non-toxic material. Over hanging branches above the catchment surface should be removed

Taps or draw-off pipes on tanks should be atleast five centimeters above the tank floor (more if debris accumulation rates are high). A tank floor sloping towards the sump can greatly aid tank cleaning as will a well-fitting access manhole.

Wire or nylon mesh should cover all inlets to prevent any insects and other creatures from entering the tank. The tank must be covered and all light excluded to prevent growth of algae and other organisms. The grill at the terrace outlet for rainwater arrests most of the debris carried by the water from the rooftop like leaves, plastic bags and paper pieces.

A coarse filter and/or foul flush device should be fitted to intercept water before it enters the tank for removing leaves and other debris.

b. Operation and maintenance: Proper operation and maintenance of rainwater harvesting systems helps to protect water quality in several ways. Regular inspection and cleaning of catchment, gutters, filters and tanks reduce the likelihood of contamination. Water from other sources should not be mixed with that in the tank.c. Treatment: Treatment of stored rainwater only makes sense if it is done properly and if hygienic collection and use of the water will ensure it does not suffer from re-contamination. There are several types of treatment possible, the most common being chlorination, boiling, filtration and exposure to ultraviolet or natural sunlight.

i) Chlorination: Chlorination is most appropriately used to treat rainwater if contamination is suspected due to the rainwater being coloured or smelling bad. It should only be done if the rainwater is the sole source of supply and the tank should first be thoroughly inspected to try to ascertain the cause of any contamination. Chlorination is done with stabilised bleaching powder (calcium hypochlorite - CaOCl2) which is a mixture of chlorine and lime. Chlorination can kill all types of bacteria and make water safe for drinking purposes. About 1 gm (approximately 1/4 tea spoon) of bleaching powder is sufficient to treat 200 litres of water.

ii) Chlorine tablets: Chlorine tablets are easily available in the market. One tablet of 0.5 g is enough to disinfect 20 litres (a bucketful) of water.

iii) Boiling: Boiling is a very effective method of purification and very simple to carry out. Boiling water for 10 to 20 minutes is enough to remove all biological contaminants.

iv) Direct sunlight: This can also be used to kill many of the harmful bacteria in water by exposing it in clear glass or plastic bottles for several hours. Although feasible in some circumstances, the water must be clear, the weather fine and the water cooled overnight before consumption.SODIS: Solar disinfection method uses sun's ultra-violet (UV) radiation to improve the microbiological quality of drinking water. It has been proven that synergies induced by radiation and thermal treatment have a significant effect on the die-off rate of microorganisms. The processes involved are indicated in the illustration.

Clean the bottle well

Fill the 3/4th of the bottle with water and cap it

Shake the bottle well

Keep the bottle on black iron sheet for minimum 6 hours in sunlight before consumption

Functioning of Sodis depends on the following factors:1) Weather and climate: Sodis requires sun's radiation and temperature to purify drinking water. The container needs to be exposed to direct sunlight for about six hours. If the temperature raises above 50 degrees Celsius, the disinfection process is three times faster. If weather conditions are not optimal the efficiency of the disinfection process can be increased by using half-blackened plastic bottles, which achieve approximately 5 degrees C higher water temperatures than fully transparent, non painted bottles. Placing the plastic bottles on a black corrugated zinc sheet would also help in achieving disinfection

Water Turbidity: Suspended particles in the water reduce the penetration of solar radiation into the water and protect microorganisms from being irradiated. Sodis requires relatively clearer water with a turbidity ofless than 30 NTU (Naphelometric Turbidity Unit - naphelometer is a modern commercial instrument used to measure turbidity)

Material: Various types of transparent plastic materials are good transmitters of light in the UV and visible range of the solar spectrum. Plastic bottles made of PET (PolyEthylene Terephtalate) are preferred because they contain less UV- stabilizers than PVC (Poly Vinyl Chloride) bottles.

Shape of containers: More the area of bottle exposed to sunlight, more would be efficiency in achieving disaffection.

Oxygen: Sodis is more efficient in water containing high levels of oxygen. Shaking a water container which is about 3/4th full for about 20 seconds before they are filled completely could increase oxygen levels. On reacting with this water, sunlight produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides). These reactive forms of oxygen kill microorganisms

Although Sodis can neither treat turbid waters nor change the chemical quality of water, this method is ideal to disinfect small quantities of water used for consumption.For more details: www.sodis.ch

Tips to ensure quality of harvested rainIt is extremely important to maintain the rainwater harvesting systems regularly for high quality performance. Following aspects should be taken care of:

1. Just before the arrival of monsoon, the rooftop/catchmet area has to be cleaned properly.

2. The roof outlet on the terrace should be covered with a mesh to prevent entry of leafs or other solid waste into the system.

3. The filter materials have to be either replaced or washed properly before the monsoon.

4. The diversion valve has to be opened for the first 5 to 10 minutes of rain to dispose off the polluted first flush.

5. All polluted water should be taken away from the recharge structures.

6. The depth of bores (of recharge structures) shall be finalised depending on the actual site condition

How much will it cost to catch rain?When community come together to harvest rain, the per-capita investment goes down. For instance, Panchsheel Park Colony about 1000 residents pooled inRs 4.5 lakh to harvest more than 170 million litres of water annually. Rainwater harvesting methods are site specific and hence it is difficult to give a generalised cost. But first of all, the major components of a rainwater harvesting system - rain and catchment area - are available free of cost. A good proportion of the expenses would be for the pipe connections. By judiciously fixing up the slopes of roofs and location of rainwater outlets, this could be brought down considerably. However the cost varies widely depending on the availability of existing structures like wells and tanks which can be modified and used for water harvesting.

Typically, installing a water harvesting system in a building would cost between Rs 2,000 to 30,000 for buildings of about 300 sq. m. The cost estimate mentioned above is for an existing building. For instance, water harvesting system in the CSE building in Tughlakabad Institutional Area, Delhi, was set up with an investment of Rs 30,000 whereas those in the model projects ranged between Rs 70, 000 and Rs 8 lakh. The costs would be comparatively less if the system were incorporated during the construction of the building itself. Some basic rates of construction activities and materials have been given here, which may be helpful in calculating the total cost of a structure. The list is not comprehensive and contains only important activities meant to provide a rough estimate of the cost.

a. Unit cost of construction activities.

Item

Unit

Rate (Rs.)

Excavation in soils

cu. m.

90.00

Excavation in rock

cu. m.

150.00

Brickwork with cement mortar (1:6)

cu. m.

1400.00

Plain cement concrete (1:3:6)

cu. m.

1500.00

Reinforced cement concrete (1:2:4) cu. m. 4700.00Including steel bars, shuttering etc.

cu. m.

4700.00

PVC piping for rainwater pipes- 110 mm diameter- 200 mm diameter

Metremetre

165.00275.00

Making borehole in metre 165.00Soft soil (with 150 mm diameter PVC casing)

metre

180.00

b. Ferrocement tanks with skeletal cage

Capacity of rooftop water harvesting system in litres

5,000

6,000

7,000

9,000

10,000

Total cost in rupees

12,430

12,975

13,970

14,380

15,800

Source: Action for food Production and United Nations Children's Fund, Rooftop rainwater harvesting systems

c. Plastic tanks: Available as finished products in various capacities. The cost of these tanks ranges from Rs 2/litre to about Rs 3.5/litre.

Other brands available in the market

Brand name

Unit cost (Rs. Per litre)

Hindustan, Jindal

1.80

Storex, Ganga

2.75

Chennai The city of Chennai faced a serious water crisis in the late 1980s. The need for effective groundwater management along with the management of surface runoff became a necessity. Moreover, extraction of groundwater started ringing alarm bells when groundwater in the north-western coastal belt indicated that there was a rapid ingress of seawater which extended from three kilometres inshore in 1969 to seven kilometres in 1983 and nine kilometres in 1987. Groundwater levels within the city also fell and brackish water began to appear even in localities which earlier had good quality groundwater sources.

Practices in rainwater harvesting: Chennai receives an average annual rainfall of 1200 mm. It receives most of the rainfall from south-west and north-east monsoons. The geology of Chennai comprises mainly of clay, shale and sandstone (sand stone formation is the main water-bearing aquifer) Harvested rainwater is mostly used for recharging of aquifers, but in some places water is stored and used for non potable purposes. Normally a building is constructed in the centre of the plot and an open area is paved with concrete. The runoff from these areas is collected through structures like percolation pits, trenches and collection wells.Impacts: In the southern coastal aquifer area, the groundwater level in 1988 was around eight metres. A gain of 4.0 to 5.0 m was established in the 20 km stretch along the southern coast. In Anna Nagar, a significant difference was observed between areas where rainwater harvesting had been undertaken and where there were no such efforts. For the city as a whole, the average water level has increased from 6.8 m in 1987 to 4.55 m in 1998. MWEB graoh2 p-197/198

Structures commonly found in Chennai

Source: Making Water Everybody's business

Recharge trenches:To prevent the runoff from paved areas of the road, a kerb is made at the gate which diverts the water into a trench within the plot. This trench is 229 mm wide, constructed around the periphery of the plot. The depth varies from 114 mm near the gate and 457 mm in the rear. As the trench is sloped towards the rear of the plot the water gets filled in the trench. As the trench is filled with the water there will be a constant water head for the percolation bore pit. Any excess water from the trench overflows into the sandy bed at the corner of the building and percolates into the well.

Percolation pits: To enable the water collected to percolate and disperse back into the sub-soil, boreholes 254 mm in diameter and 5.56 m in depth are made at three metre intervals with collection chambers. The borehole is filled with broken bricks and sand. A collection chamber of size 457 mm x 457 mm x 457 mm size is provided on top which is filled with broken bricks and a silt arrester.Recharge of dugwells: F-133

Source: Making Water Everybody's business

For recharging the well, the rainwater pipe can be connected to the open well to divert the rainwater from the terrace into the well through rainwater downtake pipes. The rainwater falling around the open space surrounding the building can be diverted to the front gate where a gutter is provided for a depth of 457.2 mm and a width of 609 mm with perforated slabs. The rainwater collected in the gutter in front of the entrance is discharged into another recharge well of 914.4 mm diameter and 6.9 m depth, provided nearby through necessary piping arrangements.

Case StudiesProjects implemented by R Jeya Kumar, Rajparis Civil Construction Company 1. Rainwater harvesting at Kones Elevator FactoryWater harvesting has been successfully used to address the issues of water scarcity and flooding caused by rainfall in the factory premises. A combination of recharge and storage was adopted at the site. A major rainwater pipe leads the rainwater from the roof to a gutter on both sides of the building. As the water comes through the roof, it is collected in a proposed storage well and then diverted into the existing service sump (of approximately 7,000 litre capacity). The overflow is taken to a percolation pit. Four rainwater harvesting percolation bore pits were proposed at the car park where water stagnates during rain. Total estimated cost of construction is around Rs. 75,000.2. Kuil Thottam: A slum in Chennai Kuil Thottam, a slum settlement in Santhome, Chennai is meeting substantial part of its daily water requirements through rainwater harvesting. The rainwater harvesting technology adopted here as a 'model project' by Rotary Club of Madras Central and Jeyakumar incorporates a catchment area of approximately 1.85 m x 1.85 m on the terrace. The accumulated rainwater is diverted to a separate water pipe, which directs the flow into the filtration tank. The water then passes through the filtration tank and after decontamination, flows into a main tank. The stored water is being used for all domestic applications after chlorination and boiling. The tests done by Rotary Club of Madras Central and Chennai Metropolitan Water Supply and Sewage Board (CMWSSB) indicated that the quality of water was better than borewell or tap water. Based on the success of the 'Model Project', water harvesting was undertaken in a catchment area of 6 m x 6 m. Runoff is diverted to a filtration tank with a capcity of 200 litre and finally to a storage tank with a capacity of 3,000 litres capacity. Periodic chlorination is done to obtain bacteria free drinking water. The total cost of the water harvesting structure installed at Kuil Thottam is Rs. 100, 000 at the rate of Rs. 4,200 per tenement.Projects implemented by Ramani R. Ramani, resident of Korattur has evolved various methods of water harvesting at his residence. Runoff from 100.0 sq.m of area is collected out of which rainwater from 50.0 sq. m is used for domestic purposes. Remaining quantity is used for gardening and to recharge groundwater recharging the well through a recharge pit and for watering the garden. He has resurfaced his roof with Mangalore terrace tiles to generate a mild slope to the lentil level storage tank with a capacity of about 3,000 litres.

To keep this tank free from microbial contamination he has mixed a waterproofing chemical with the cement slurry to give an acrylic-poly-sulphate cement slurry coating. Through simple treatment and later filtering through 'Aqua -Guards' a commercially available water purifying product that kill germs, the rainwater is used for drinking and kitchen purposes. Each filling of the tank can sustain the drinking and kitchen needs for about 2 months. In a year the tank gets filled four to five times. Sometimes, the tank gets filled up more than once in a week. During these times, the excess water is diverted to recharge the groundwater aquifer. Ramani had to invest Rs. 8,000.00 in this project which was implemented in 1994.

Civic Authority's Initiatives: In order to facilitate groundwater management, the Chennai Metropolitan Area Groundwater (Regulation) Act was passed in 1987. Metrowater was identified as the enforcing authority for multistoried buildings/special buildings. They issued instructions that no new water connection be given unless water harvesting structures provided in the approved plan were implemented.

A series of investments were made by Chennai Metrowater from 1991 onwards to harvest floodwaters along the course of the rivers bordering the city. Three checkdams were constructed at Valliyur, Jagnathapuram and Melsembedu in 1991, 1992 and 1995 respectively. Moreover the government agencies are involved in implementing rainwater harvesting structures in public places like parks, roads, fly overs, and storm drains. Thus every possible catchment is being utilised for water harvesting. As of now 400 buildings, 216 schools and 56 parks owned by the corporation of Chennai has the rainwater harvesting systems installed in it.

PIX: Fly over.

TWAD's initiatives TWAD Board has taken steps to implement the rain water harvesting structures in TWAD board building with a rooftop area of 2000 sqm. The calculated water harvesting potential of this building is 14.4 lakh litres, which is expected to serve water supply for 144 days for the staff and visitors.

There are about 12 rainwater pipes are drained out through 3 recharge trenches and a recharge well. The recharge trench is 10 m in length, 1.0 m wide and 2.0 m deep. The bottom of the trench is filled with 60 cm of pebbles followed by coarse sand upto 1.20 m. Three unlined recharge bores of 150 mm diameter are drilled inside the trench each to a depth of 4.0 m feet and filled up with pebbles. Three of the rainwater pipes are connected to each trench.

Practitioners:

R JeyakumarManaging DirectorRajparis Civil Constructions LtdRaj Court, 162-B, Greams Land Thousand LightsChennai - 600006Tel: 044-8290038, 8290566, 8295627, 8294931Fax: 044-8265949

R. RamaniManaging TrusteeRAMADIES Charitable Trust5 (1050), 41st StreetTNHB Colony, KoratturChennai 600080Tel: 044 - 6523310Email: ramadies2K@usa.net, ramani6242@usa.net

Dr. Sekhar Raghavand-15, Bayview ApartmentsKalakshetra ColonyBasant NagarChennai 600090Tel: 044-4918415Fax: 044-4901360Email: ashoksekhar@yahoo.com

Ms. Santha Sheela NairIAS, SecretaryDepartment of Home Affairs (Government of Tamil Nadu)SecretariatChennai 600009Tel: 044-5361113Fax: 044-5360596

Dr. Nirmal SenguptaProfessorMadras Institute of Development Studies (MIDS)79 second Main Road Gandhi NagarChennai 600020Tel: 044- 4411574, 4412589, 4412295, 4419771Fax: 044- 4910872Email: nsengupt@eth.net

B UmapathiScientist 'B'Central Ground Water Board (CGWB)South Eastern Coastal RegionE-1, Rajaji BhavanBesant NagarChennai 600090Tel: 044- 4914494Fax: 044- 4914334Email: cgwb@tn.nic.in

K R GopinathPromoterRain Water HarvestingK R G Rainwater Harvesting CompanyAA-98 Anna NagarChennai 600040Tel: 044-6284960, 6283831Fax: 044- 6285615Email: rakki@giasmd01.vsnl.net.inWebsite: www.webindia.com/pmf

Prof B S ThandaveswaraProfessorEnvironmental and Water Resources EngineeringIndian Institute of Technology (IIT)Department of Civil EngineeringChennai 600036Tel: 044- 4458292Fax: 044- 2350509, 2352545Email: thand@civil.iitm.ernet.in, thandb@hotmail.com

Bharath JairajLegal CoordinatorConsumer Action Group(CAG)7, Fourth Street Venkateswara Nagar, AdyarChennai 600020Tel: 044- 4914358, 4460387Fax: 044-4914358Email: cag@xlweb.com

Dr. Goutam GhoshPrincipal CorrespondentThe Hindu859-860, Anna SalaiChennai 600002Tel: 044-8413344 Ext536Fax: 044-8415325Email: goutam@thehindu.co.in

Prof A VaidyanathanProfessor EmeritusMadras Institute of Development Studies (MIDS)P O Box 94879, Second Main RoadGandhi Nagar AdayarChennai 600020Tel: 044-4411574, 4412589, 4412295, 4419771Fax: 044- 4910872Email: vaid123@md4.vsnl.net.in

D S Ramakriashna RaoArchitectVisiting FacultySchool of Architecture & PlanningAnna UniversityDesirazu Associates No 9, 1st StreetBalaji NagarChennai 600014Tel: 044-8231695Fax: 044- 8283960Email: aarkay54@yahoo.comWebsite: www.chennaiarchitect.com

Dr. Kodumudi ShanmugamRetd. Superintending EngineerAU - PPST CentreAnna UniversityChennai 600025Tel: 044- 2301896Email: ppstau@yahoo.com

http://www.rainwaterharvesting.org/Solution/Solution.htm