nahrim's experiencein rainwater utilisation system research-slides[1]
TRANSCRIPT
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
1/13
NAHRIMS EXPERIENCE IN
RAINWATER UTILISATION SYSTEMS RESEARCH
Ahmad Jamalluddin bin Shaabanand Huang Yuk Feng
National Hydraulic Research Institute of Malaysia (NAHRIM)
Water Resources Management Division
Lot 5733, Jalan Putra Permai, 43300 Seri Kembangan, Selangor
ABSTRACT
With the global change in weather patterns affecting rainfall distribution temporally and
spatially, rainwater harvesting and utilization has certainly be given an added dimension and approach
towards an integrated environment friendly and sustainable urban water resources developmentinitiative. With the advantage of the countrys blessed generous rainwater resources, capturing it for
present and future use on-site would undoubtedly help to supplement city public water supply and
possibly replacing the non-potable common whilst also reducing the potential of urban flash floods via
reduction of peak storm runoff. Consequently, NAHRIM has carried out three main pilot projects forrainwater harvesting, which include (i) a double storey terrace house located at Taman Wangsa
Melawati, Kuala Lumpur, (ii) a mosque complex at Taman Bukit Indah, Ampang, and (iii) theHeadquarters of the Department of Irrigation and Drainage (DID) in Kuala Lumpur, in collaboration
with DID. Harvested rainwater of the projects is used for non-potable purposes only. This paper is
aimed at discussing the R&D on rainwater systems carried out by NAHRIM with focus on systemdesign, installation cost and unit cost, deployed for the double storey terrace house at Taman Wangsa
Melawati and the mosque complex at Taman Bukit Indah. The amount of rainwater use and its
reliability from the NAHRIM in-house studies are explained. The various benefits of rainwater, issues,
strategies and future plans for rainwater harvesting and utilisation are also presented.
1.0 INTRODUCTION
Rainwater harvesting and utilization has been practiced in Malaysia especially in the villages since
long ago. Subsequent to the 1998 April drought, the Minister of Housing and Local Government on 7May 1998 has expressed the Governments interest for houses to be designed to include facilities for
collecting rainwater. In 1999, the Ministry of Housing and Local Government has produced a
Guideline on Installing a Rainwater Collection and Utilization System (Rainwater Guideline, 1999).This guideline is intended as an ideas manual for reference for those who want to install a rainwater
harvesting and utilization system. It aims to encourage the owners to think and adopt wherever
possible appropriate innovative alternatives which offer real advantages and adaptable to their needs.
In support of the Government's interest in rainwater harvesting, NAHRIM through its
collaboration with other government agencies such as the Department of Irrigation and Drainage(DID), the Department of Local Government (JKT), Universiti Teknologi Malaysia (UTM), Universiti
Sains Malaysia (USM), Universiti Putra Malaysia (UPM) and Universiti Malaya (UM), has been
pursuing R&D on rainwater harvesting with focus on system design and installation cost, systemperformance and system operating and maintenance cost, unit cost, effectiveness in reducing the urban
flash flood problems, and policies, by-laws and proposing incentives for system implementation.
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
2/13
2
2.0 RAINWATER HARVESTING SYSTEM AT A DOUBLE STOREY TERRACE HOUSE
The rooftop has cement tiles and has a roof area of 60 m2. The rainwater is conveyed from the rooftop
to the storage tanks via a series of gutters and pipes. Rainwater from the rooftop is usually
contaminated with dirt, bird droppings, leaves, etc. The first flush of rainwater from the roof surface is
directed into the first flush tank of 200 litres to filter out these materials from the rainwater before it is
stored in the ground floor storage tanks.
For the 1st
phase of the study, two black High Density Polyethylene (HDPE) tanks with a 2500liter capacity each were installed as storage tanks. The water use and quality are monitored over one
year. In the 2nd
phase, these two black HDPE tanks are replaced with a better storage tank design
taking into consideration the aesthetic and utility aspects. It is a brick storage tank of 5000 litrescapacity and the space above the tank is used as a childrens play area and also for drying clothes (See
Figures 1a, 1b and 1c). 3300 litres of storage is allocated for rainwater reuse (bottom portion), while
1700 litres is for detention storage (top portion). A 1.0 horsepower electric pump with minimum headof 12 m was installed to pump water from the ground storage tank to the roof rainwater tank. This tank
was installed on the roof in addition to the existing potable water roof tank that is a mandatory
requirement. The additional tank has a separate rainwater supply for non-potable household use. Thestudy house also has a separate plumbing system to cater for the rainwater usage. Since rainwater was
to be used for non-potable use, the plumbing system was installed in such a way that there was a
bypass connection for each flushing cistern. In case of water shortage or non-availability of rainwater,
the public water supply can be switched on. The rainwater plumbing system was also connected to thewashing machine pipe and pipe for general cleaning.
2.1 USE AND RELIABILITY OF RAINWATER
The occupants of the house under study include two adults and four school going children. The house
has three bathrooms. The amount of rainwater used for facilities was monitored with mechanical watermeters in each facility. Readings are taken and recorded manually. The water use figures obtained are
comparable with water use figures from literatures and specifications of the respective products. Table
1 shows average water use for facilities using rainwater based on twelve months data. Since there wasno treatment to the rainwater collected, it is strictly used for toilet flushing, general washing and
washing clothes.
Table 1: Rainwater Use for Various Facilities
ItemAveragedaily use(liters)
AverageMonthly use
(liters)%
Washing clothes 300 9,000 66
Toilet Flushing(3 W.Cs)
90 2,700 20
General Cleaning(including car andmotorcycle washing)
65 1,950 14
TOTAL 455 13,650 100
(Source: Shaaban and Appan, 2003)
Monthly Rainwater use = 13,650 liters
Monthly water use (from public water supply) = 27,000 litersTotal Monthly Household Water Use = 40,650 liters
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
3/13
3
From the above, household use for non-potable purpose using rainwater contributes 34% of the total
monthly household water use.
A simulation model was developed and used to check on the reliability of the rainwater harvesting
system based on the 5 m3
storage tanks and water demand of 455 liters/day. The model was run using
15 years of daily rainfall data from DID Ampang. The rainfall characteristics are tabulated below:
Table 2: Rainwater Use for Various FacilitiesThe average annual rainfall 2,542 mm
The highest daily rainfall 166 mm
The longest period without rain 29 days
Average period without rain 15 days
(Source: Shaaban and Appan, 2003)
The parameters specified for the simulation model were as follows:Size of roof = 60 m
2.
Run-off coefficient = 0.80
First Flush = 1 mm of rainfall or approximate 60 litres.
No. of persons = 6Average usage per person per day = 75.8 litres.
Total water usage per day = 455 litres
Simulating with these parameters, the reliability of the system was found to be 66.2% for a
water use of 455 litres/day and storage of 5 m3. To attain 74% reliability the storage need to be
increased 8 times i.e. up to 40 m3. With the limited roof area, a big increase in storage would result in
only a small increment in reliability. One possibility of further increasing the system reliability is to
increase the roof area (using the other half of the house roof estimated at another 60 m2) so as to catch
more rainfall and thereby increase the yield. This necessitates installation of extra gutters, piping,storage tanks and a pump.
2.2 ECONOMIC ASPECTS SYSTEM COST AND UNIT COST
From a project cost evaluation by NAHRIM, the system cost and unit cost for the rainwater cum
detention storage system (brick tank) for a double storey linked house (Taman Wangsa Melawati,Kuala Lumpur) is as follows:
Table 3: System Cost for the Rainwater Cum
Detention Storage System - Brick TankComponents Amount (RM)
Gutter (uPVC) 150.00Conveyance System 200.00
Plumbing works 400.00Water tank (top) 200.00Brick tank (ground) 5000 liters capacity 2,600.00Water pump (electrical) 750.00
TOTAL 4,300.00
(Source: Shaaban and Appan, 2003)
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
4/13
4
In working out the unit cost of water for the system, the life expectancy of the system is taken as 25
years. The operating cost includes O&M of the pumps and electricity. The unit cost of water was thenworked out to be RM 2.63/ m
3
The current water tariff for domestic households (Kuala Lumpur and Selangor) is RM 2.00 for water
consumption above 35 m3
per household per month. However, there seems to be an imminent increasein the near future. It can be seen that the unit cost of rainwater cum detention storage system at RM
2.63/m3 is 1.3 times much higher than that of piped water. As practiced in Japan and elsewhere, the
Government may need to provide subsidies to encourage the public to install rainwater cum detentionstorage systems.
3.0 RAINWATER HARVESTING SYSTEM AT A MOSQUE COMPLEX
The rainwater collected is stored in the storage tank (underground) and pumped to the toilets and
standpipes. The system component consists of a catchment subsystem, filtering cum conveyance
system, storage subsystem, pumps, and internal plumbing. The schematic arrangement of the systemand the site plan of the mosque are shown in Figures 2 and 4, respectively.
Catchments Subsystem
For this rainwater harvesting system, part of the rooftop and also a portion of the mosque compound is
the catchments subsystem. For non-potable use, any roofing material can be used as the catchmentssubsystem. The roof material used in the study is of metal tiles. The roof area of the mosque utilised
is 644 m2
and the mosque compound area utilised is 2925 m2.
Conveyance System
The function of this subsystem is to convey the rainwater roof runoff and the filter the storm runoff
from the catchments sub-system to the underground storage tank. Basically this subsystem consists of
3 main components. These components are the gutter, downspouts and the conveyance pipes (filterstrips covered with geotextile called hydronet) placed in the concrete drains. Rainwater from the
rooftop is channeled to the gutters and then through the downspouts and finally through theconveyance pipes to the storage tank. While the storm runoff is channeled to the filtering cum
conveyance pipes to the storage tank. The gutters were incorporated in the design. It is concealed and
and formed as part of the pillar of the mosque. There were several downpipes provided to cater for therainwater. At the downspout inlet a net is placed. The net is to trap rubbish, leaves and other debris
usually found on rooftops.
Underground Storage Tank
The collected rainwater is stored in the underground storage tank (Figure 3) via the conveyance pipeafter the filtration by the filter strips. The storage tank is constructed using polyethylene moduleswrapped in geotextile called hydronet and an impermeable HDPE liner. The underground storage tank
could withstand loads of up to 40 KN/ m2, as above it is the mosque car park. An overflow pipe is
provided to cater for storm inflow of 10 year return period.
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
5/13
5
Submersible Pumps
Two submersible pumps (2HP), one to be operational and the other one as a back-up (variable speed
motor to ensure immediate response to the demand flowrate) are used to pump rainwater from the
underground storage tank to the toilets and stand pipes for general cleaning and gardening purposes.
The submersible pump was chosen since it does not pose any suction problems (one of its advantage).
A pressure vessel (pressure set at 8 bar) is placed after the submersible pump to maintain constantpressure (1 bar) at the outlet.
Backup Water from Water Supply Department (WSD)
In case the rainwater in the storage tank is insufficient during dry periods, supply from WSD would befed automatically to the rainwater storage tank. This would ensure uninterrupted water supply to the
system. Similarly, if there is a blackout and electricity is not available for the pumps to operate then
the public water supply would come on automatically to the toilets.
Plumbing System
The plumbing system is independent from the public water supply as per requirements of WSD. For
potable use (cooking and drinking), water supply must be direct from WSD. As practiced in overseas
country, color coding is used on the plumbing system to distinguish between municipal water supply
and supply from rainwater. Signage were also provided at the toilets and standpipes to inform thatrainwater is used and reminding the public that the rainwater is not meant for drinking purposes.
3.1 PROBLEMS ENCOUNTERED DURING AND AFTER CONSTRUCTION
Initially the conveyance pipe is intended to channel the roof runoff only but as this is a retrofitting job
and the mosque committee stipulates no hacking of the concrete perimeter drains, the use of filterstrips wrapped with hydronet was adopted to serve as the filter cum conveyance pipe. Additional
storm runoff from the mosque compound is also channelled into the filter cum conveyance pipes.
Incorporating the storm runoff from the mosque compound has its disadvantages. During
heavy rainstorms there could be overflow of sewage from the toilets that could pollute the storm
runoff.
3.2 USE AND RELIABILITY OF RAINWATER
The peak daily water demand is estimated at 15,000 litres based on 2,500 persons utilizing 6 litres pertoilet flush. The total peak daily water demand of the mosque for wudhu, toilet flushing and general
cleaning is estimated at 26,250 litres.
Utilizing 15 years of rainfall data from Department of Irrigation and Drainage (DID) Ampang
and inputting the daily water demand, catchment area and appropriate runoff coefficient to a simple
simulation model, the reliability (where Reliability = Delivered volume of rainwater / DemandVolume) of the system was found to be 60 %.
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
6/13
6
3.3 ECONOMIC ASPECTS SYSTEM COST AND UNIT COST
System cost includes supply and installation and varied accordingly depending to the type of materials
used. Since the gutters were already incorporated in the design of the mosque, the additional costs for
rainwater utilization were the costs of underground storage tank, conveyance pipes, pumps with sensor
and additional plumbing separated from the WSD water supply system. A breakdown of the cost of
the various components of the system in Malaysian Ringgit (RM) is presented in Table 5.
Table 5: Cost of System Components_____________________________________________
Conveyance System to cater for stormwater (modification) RM 15,000
Plumbing works RM 5,000Underground Water Tank (60 m
3capacity) RM 60,000
Water pumps including sensor RM 15,000
TOTAL RM 95,000
___________________________________________________________________________
In working out the unit cost of water for the system, the life expectancy of the system is taken as 25years. The operating cost includes O&M of the pumps and electricity. The unit cost of water was then
worked out to be RM 1.26/ m3.
3.4 MAINTENANCE OF THE SYSTEM
Maintenance of rainwater equipment is necessary to ensure that clean rainwater is collected and used.
Pertinent aspects of maintenance involved are as follows:i) Catchment area clean regularly leaves, trash and animal excreta in catchment areas including
roofs.
ii) Filter cum conveyance pipes need to be checked periodically and replace damaged hydronetas required.
iii) Rainwater storage tanks Internal inspection carried out twice a year. The inside cleaned asrequired.
iv) Rainwater supply equipment Mechanical devices such as pumps are checked at least everythree months. Other devices should be checked every six months and maintained the same way
as public water supply equipment.
4.0 BENEFITS OF RAINWATER HARVESTING
The benefits of rainwater harvesting system to the country are many and can be broadly grouped intothe following:
(i) Rainwater utilisation for non-potable use can reduce the dependence and demand of publicwater supply;
(ii) The water saving would result in reduction of the water bill. With increases in water tariffthe future monetary savings from the Rainwater Harvesting System (SPAH) would be even
more attractive;(iii) According to the research carried out by NAHRIM on the SPAH pilot project for a double
storey terrace house located at Taman Wangsa Melawati (Shaaban and Appan, 2003),
SPAH is able to save up to 34% of public water use, in addition to the 10% of reduction inpeak discharge by assuming every terrace house has been installed with the same SPAH
(covers 19% of total catchment area). Further reduction of peak discharge, up to 50%, could
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
7/13
7
be achieved by installing rainwater cum detention storage systems in the shophouses,
multipurpose hall, mosque, kindergarden and park, in this housing area. Reduction of peakdischarge not only reduces the needs of drainage system upgrading but also reduces the
impacts of flash floods and erosion. Erosion and flooding due to runoff from impervious
areas such as pavement and roofs will be reduced by rainwater harvesting as some rain is
instead captured and stored.
5.0 ISSUES IN IMPLEMENTING SPAH
The issues in implementing the rainwater harvesting systems in the country include:
(i) The lack of understanding of the public about the concept of rainwater utilisation;(ii) Aspects of design for locating rainwater equipment (example: downpipes, tanks and pumps)
not given consideration with respect to aesthetics of the environment, space savings and
ease of maintenance;
(iii) In the view of health aspects, breeding of mosquitoes can occur in pools of stagnant waterin gutters and also the rainwater tank (need to ensure gutters have adequate slope and
cleaned when necessary and prevent entry of mosquitoes into rainwater tanks and
introducing Abate or similar chemicals to kill mosquito larvae)
6.0 CONCLUSIONS
From the study on the double storey terrace house, the rainwater systems could meet up to 34% of thedomestic non-potable household water requirements at 65.5% reliability (for storage of 5000 litres) and
61.4% reliability (for a storage of 3300 litres) respectively. The unit cost of rainwater (with detention
storage) at RM 2.63/m3
is more costly compared with the piped water cost at RM 2.00/m3
for waterconsumption above 35 m
3per household per month.
10% reduction in peak storm runoff is achieved when rainwater cum detention storage systemsare installed at all the houses. Further reduction, up to 50%, in peak storm runoff could be possible
when the rainwater cum detention storage systems are extended to the shophouses, mosque,
kindergarten and parks/lawns in the housing area. Furthermore, the rainwater cum detention storagesystems for the park could be used for plant watering, firefighting and emergency use for the
community during a prolonged drought.
Based on the study on a mosque complex, it is possible to use rainwater for toilet flushing (with
60% reliability) which at the same time could save up to 34% of the public water supply annually. The
unit cost of rainwater at RM 1.26 per m3
is considerably higher compared to the water rate for religious
institutions (which is given special low tariff by the government). Nevertheless, such rainwatersystems when applied extensively to public and private buildings will reduce significantly the
dependence on public water supply thus contributing towards sustainable water resources development
especially in the rapidly growing urban areas of Malaysia.
Rainwater harvesting and utilisation especially in urban areas is likely to increase in future due
to its multifarious benefits such as reducing pressure on existing water supply systems and reduction ofurban floods. With its domestic and environmental benefits, rainwater harvesting systems could
become a standard feature of future homes and buildings supplementing the water needs of its
occupants. Issues arising from the implementation of SPAH should be handled with great care. Theeconomic benefits in terms of reducing the costs of urban flood mitigation works and downstream
damage reduction needs further investigation.
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
8/13
8
8. REFERENCES
Rainwater Guidelines, 1999. Guidelines for Installing a Rainwater Collection and Utilisation System,
Ministry of Housing and Local Government, Malaysia.
Shaaban, A. J. and A., Appan, 2003. Utilising Rainwater for Non-potable Domestic Uses and
Reducing Peak Urban Runoff in Malaysia, International Rainwater Cistern Systems Conference,Mexico
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
9/13
9
Figure 1a: Front View of Rainwater Harvesting cum Detention Storage System.
Figure 1b: View of Rainwater Harvesting cum Detention Storage System from the front of the house.
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
10/13
10
Figure 1c: Various components of the Rainwater cum Detention Storage System
Gutter and down pipe from
roof
First flush tank
Rainwater cum detention storage tank
View of the Rainwater System
from the front of the house
Gutter leading to first
flush tank
1 HP electric pumpRainwater connection for
washing machine
Rainwater connection
for toilet flushing
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
11/13
Figure2:SchematicA
rrangementoftheRainwater
System
Figure2:SchematicA
rrangementoftheRainwater
System
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
12/13
Figure3:Underground
StorageTank(Cross-section)
Figure3:Underground
StorageTank(Cross-section)
-
8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]
13/13
Figure4:SitePlanoftheMos
que