RAINWATER HARVESTING AND GREYWATER RECYCLING IN URBAN AREAS – THE CHENNAI EXPERIENCE

Seetha Gopalakrishnan

India Water Portal

Rainwater Harvesting - Basics

Is this a novel concept? Not a new technology or an alternative Adaptations - Traditional vs. Modern designs

Why should I harvest rainwater? No. of rainy days are less – around 60-90 days on an average across India Cities are usually water starved, not rain starved Needs - Immediate use vs. Groundwater recharge

Is it expensive? Not very if it is incorporated in the original design

How do I go about this? Harvest rainwater, both from the roof-top as well as around the building – Simple design

Rooftop Rainwater Harvesting

Terrace down-take pipes → Underground sump │Overflow from the sump → Dug well If dug wells are absent, construct recharge wells or percolation pits depending upon space

available

Assume that 60% of the total rainfall is effectively harvested

Volume of. water harvested = 1,30,000 x 0.6 = 78,000 litres

213 litres of water/day will be available for the household

This is enough to meet the drinking and cooking needs of a household

Consider a building with a flat terrace area of 100 sq.m.

Average annual rainfall in Chennai is approximately 1300mm

Diversion of rainwater from the terrace into a shallow dug well in an

apartment complex

Harvesting the Driveway Runoff

Rainwater that falls around the building is usually wasted Not good for potable uses, but definitely worth using for recharge Gutter near the gate does the trick Water collected at the gate → Recharge well

Greywater Recycling

Daily Water Usage

Flushing - 35%Kitchen - 15% Bathing and Washing of Clothes - 50%

•Almost 60% of the refuse water from our daily usage is good, quality sterile water - Can be easily cleaned up •Plants remove all the organic material•Water is further polished by soil bacteria as it travels down the soil•The cleaned water can be safely used for flushing and gardening •Excess can be put into the soil to augment the shallow water table

Characteristics of a good groundwater recharge system

Completeness -Both rooftop and driveway runoff water to be harvested. Apportioning of water–To avoid overload of any one system, leading to overflow and loss. Proper design - Volume of water likely to flow through and the nature of the soil in the area

should be considered. Maintainability - Design should incorporate features allowing for periodic maintenance of the

structure.

Both from Rainwater harvesting and Greywater recycling

The Chennai Experience

Chennai is rain-rich but water- starved No perennial river nearby Rain from SW and NE monsoons Macro-supply - Reservoirs are woefully

inadequate

What should be done? Reduce dependence on Metro water Supply Increase dependence on sources within

one’s premises Conjunctive use of aquifers – shallow & deep

Annual rainfall averaged over the last 50 years falling over the 174 Sq km area of

Chennai is 127cm.

If this is harvested, every citizen can get 135 litres per day

Government Initiatives

1) Tamil Nadu Municipal Laws (Second Amendment) Ordinance, 2003

Inserted Sec. 255A in the Chennai City Municipal Corporation Act, 1919 which made Rain Water Harvesting mandatory

Similar changes were made in Municipal laws of other major cities as well

2) Rain Water Harvesting Structures in Buildings - Amendments to Building Rules

3) Ground Water Potential Villages including Well field & Suburban Area

4) Act to amend the Madras Metropolitan Area Groundwater (Regulation) Act 1987

Rain Centre Chennai RWH Survey - 2006

•After the record rainfall of 250 cm. in 2005, there was a phenomenal rise in groundwater table

•Survey revealed that the Groundwater table had risen by minimum of 6 m. and a maximum of 8 m. in the entire city

•Shallow aquifer recharge very successful -Temple tanks which were previously empty had water in them

Tamilnadu is the first state in India to make rainwater harvesting mandatory