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Newsletter and Technical Publications
Rainwater Harvesting And Utilisation
An Environmentally Sound Approach for Sustainable
Urban Water Management: An Introductory Guide for Decision-Makers
Examples of Rainwater
Harvesting and Utilisation Around the World
Singapore
Singapore, which has limited land resources and a rising demand for water, is
on the lookout for alternative sources and innovative methods of harvesting
water. Almost 86% of Singapore’s population lives in high-rise buildings.
A light roofing is placed on the roofs to act as catchment. Collected roof water
is kept in separate cisterns on the roofs for non-potable uses. A recent study
of an urban residential area of about 742 ha used a model to determine the optimal
storage volume of the rooftop cisterns, taking into consideration non-potable
water demand and actual rainfall at 15-minute intervals. This study demonstrated
an effective saving of 4% of the water used, the volume of which did not have
to be pumped from the ground floor. As a result of savings in terms of water,
energy costs, and deferred capital, the cost of collected roof water was calculated
to be S$0.96 against the previous cost of S$1.17 per cubic meter.
A marginally larger rainwater harvesting and utilisation system exists in the
Changi Airport. Rainfall from the runways and the surrounding green areas is
diverted to two impounding reservoirs. One of the reservoirs is designed to
balance the flows during the coincident high runoffs and incoming tides, and
the other reservoir is used to collect the runoff. The water is used primarily
for non-potable functions such fire-fighting drills and toilet flushing. Such
collected and treated water accounts for 28 to 33% of the total water used,
resulting in savings of approximately S$ 390,000 per annum.
Tokyo,
Japan
In Tokyo, rainwater harvesting and utilisation is promoted to mitigate water
shortages, control floods, and secure water for emergencies.
The Ryogoku Kokugikan Sumo-wrestling Arena, built in 1985 in Sumida City, is
a well-known facility that utilises rainwater on a large scale. The 8,400 m2
rooftop of this arena is the catchment surface of the rainwater utilisation
system. Collected rainwater is drained into a 1,000 m3 underground storage tank
and used for toilet flushing and air conditioning. Sumida City Hall uses a similar
system. Following the example of Kokugikan, many new public facilities have
begun to introduce rainwater utilisation systems in Tokyo.
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| "Rojison", a simple and unique rainwater utilisation facility
at the community level in Tokyo, Japan. |
At the community level, a simple and unique rainwater utilisation facility,
“Rojison”, has been set up by local residents in the Mukojima district
of Tokyo to utilise rainwater collected from the roofs of private houses for garden
watering, fire-fighting and drinking water in emergencies.
To date, about 750 private and public buildings in Tokyo have introduced rainwater
collection and utilisation systems. Rainwater utilisation is now flourishing at
both the public and private levels.
Berlin,
Germany
In October 1998, rainwater utilization systems were introduced in Berlin as
part of a large scale urban re-development, the DaimlerChrysler Potsdamer Platz,
to control urban flooding, save city water and create a better micro climate.
Rainwater falling on the rooftops (32,000 m2) of 19 buildings is collected and
stored in a 3500 m3 rainwater basement tank. It is then used for toilet flushing,
watering of green areas (including roofs with vegetative cover) and the replenishment
of an artificial pond.
In another project at Belss-Luedecke-Strasse building estate in Berlin, rainwater
from all roof areas (with an approximate area of 7,000 m2) is discharged into
a separate public rainwater sewer and transferred into a cistern with a capacity
of 160 m3, together with the runoff from streets, parking spaces and pathways
(representing an area of 4,200 m2). The water is treated in several stages and
used for toilet flushing as well as for garden watering. The system design ensures
that the majority of the pollutants in the initial flow are flushed out of the
rainwater sewer into the sanitary sewer for proper treatment in a sewage plant.
It is estimated that 58% of the rainwater can be retained locally through the
use of this system. Based on a 10-year simulation, the savings of potable water
through the utilisation of rainwater are estimated to be about 2,430 m3 per
year, thus preserving the groundwater reservoirs of Berlin by a similar estimated
amount.
Both of these systems not only conserve city water, but also reduce the potential
for pollutant discharges from sewerage systems into surface waters that might
result from stormwater overflows. This approach to the control of non point
sources of pollution is an important part of a broader strategy for the protection
of surface water quality in urban areas.
Thailand
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Example of the rainwater jar used in Thailand.
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Storing rainwater from rooftop run-off in jars is an appropriate and
inexpensive means of obtaining high quality drinking water in Thailand.
Prior to the introduction of jars for rainwater storage, many communities
had no means of protecting drinking water from waste and mosquito infestation.
The jars come in various capacities, from 100 to 3,000 litres and are
equipped with lid, faucet, and drain. The most popular size is 2,000 litres,
which costs 750 Baht, and holds sufficient rainwater for a six-person
household during the dry season, lasting up to six months.
Two approaches are used for the acquisition of water jars. The first
approach involves technical assistance and training villagers on water
jar fabrication. This approach is suitable for many villages, and encourages
the villagers to work cooperatively. Added benefits are that this environmentally
appropriate technology is easy to learn, and villagers can fabricate water
jars for sale at local markets. The second approach is applicable to those
villages that do not have sufficient labour for making water jars. It
involves access to a revolving loan fund to assist these villages in purchasing
the jars. For both approaches, ownership and self-maintenance of the water
jars are important. Villagers are also trained on how to ensure a safe
supply of water and how to extend the life of the jars.
Initially implemented by the Population and Community Development Association
(PDA) in Thailand, the demonstrated success of the rainwater jar project
has encouraged the Thai government to embark on an extensive national
program for rainwater harvesting.
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Indonesia
In Indonesia, groundwater is becoming more scarce in large urban areas due to
reduced water infiltration. The decrease of groundwater recharge in the cities
is directly proportional to the increase in the pavement and roof area. In addition,
high population density is has brought about high groundwater consumption. Recognising
the need to alter the drainage system, the Indonesian government introduced
a regulation requiring that all buildings have an infiltration well. The regulation
applies to two-thirds of the territory, including the Special Province of Yogyakarta,
the Capital Special Province of Jakarta, West Java and Central Java Province.
It is estimated that if each house in Java and Madura had its own infiltration
well, the water deficit of 53% by the year of 2000 would be reduced to 37%,
which translates into a net savings of 16% through conservation.
Capiz
Province, the Philippines
In the Philippines, a rainwater harvesting programme was initiated in 1989 in
Capiz Province with the assistance of the Canadian International Development
Research Centre (IDRC). About 500 rainwater storage tanks were constructed made
of wire-framed ferro-cement, with capacities varying from 2 to 10 m3. The construction
of the tanks involved building a frame of steel reinforcing bars (rebar) and
wire mesh on a sturdy reinforced concrete foundation. The tanks were then plastered
both inside and outside, thereby reducing their susceptibility to corrosion
relative to metal storage tanks.
The rainwater harvesting programme in Capiz Province was implemented as part
of an income generation initiative. Under this arrangement, loans were provided
to fund the capital cost of the tanks and related agricultural operations. Loans
of US$200, repayable over a three-year period, covered not only the cost of
the tank but also one or more income generating activities such as the purchase
and rearing of pigs, costing around US$25 each. Mature pigs can sell for up
to US$90 each, providing an income opportunity for generating that could provide
sufficient income to repay the loan. This type of innovative mechanism for financing
rural water supplies can help avoid the requirement for water resources development
subsidies.
Bangladesh
In Bangladesh, rainwater collection is seen as a viable alternative for providing
safe drinking water in arsenic affected areas. Since 1997, about 1000 rainwater
harvesting systems have been installed in the country, primarily in rural areas,
by the NGO Forum for Drinking Water Supply & Sanitation. This Forum is the
national networking and service delivery agency for NGOs, community-based organisations
and the private sector concerned with the implementation of water and sanitation
programmes in unserved and underserved rural and urban communities. Its primary
objective is to improve access to safe, sustainable, affordable water and sanitation
services and facilities in Bangladesh.
The rainwater harvesting tanks in Bangladesh vary in capacity from 500 litres
to 3,200 litres, costing from Tk. 3000-Tk.8000 (US$ 50 to US$ 150). The composition
and structure of the tanks also vary, and include ferro-cement tanks, brick tanks,
RCC ring tanks, and sub-surface tanks.
The rainwater that is harvested is used for drinking and cooking and its acceptance
as a safe, easy-to-use source of water is increasing amongst local users. Water
quality testing has shown that water can be preserved for four to five months
without bacterial contamination. The NGO Forum has also undertaken some recent
initiatives in urban areas to promote rainwater harvesting as an alternative source
of water for all household purposes.
Gansu
Province, China
Gansu is one of the driest provinces in China. The annual precipitation is about
300 mm, while potential evaporation amounts to 1500-2000 mm. Surface water and
groundwater is limited, thus agriculture in the province relies on rainfall
and people generally suffer from inadequate supplies of drinking water.
Since the 1980s, research, demonstration and extension projects on rainwater
harvesting have been carried out with very positive results. In 1995/96, the
“121” Rainwater Catchment Project implemented by the Gansu Provincial
Government supported farmers by building one rainwater collection field, two
water storage tanks and providing one piece of land to grow cash crops. This
project has proven successful in supplying drinking water for 1.3 million people
and developing irrigated land for a courtyard economy. As of 2000, a total of
2,183,000 rainwater tanks had been built with a total capacity of 73.1 million
m3 in Gansu Province, supplying drinking water for 1.97 million people and supplementary
irrigation for 236,400 ha of land.
Rainwater harvesting has become an important option for Gansu Province to supply
drinking water, develop rain-fed agriculture and improve the ecosystem in dry
areas. Seventeen provinces in China have since adopted the rainwater utilization
technique, building 5.6 million tanks with a total capacity of 1.8 billion m3,
supplying drinking water for approximately 15 million people and supplemental
irrigation for 1.2 million ha of land.
Africa
Although in some parts of Africa rapid expansion of rainwater catchment systems
has occurred in recent years, progress has been slower than Southeast Asia.
This is due in part to the lower rainfall and its seasonal nature, the smaller
number and size of impervious roofs and the higher costs of constructing catchment
systems in relation to typical household incomes. The lack of availability of
cement and clean graded river sand in some parts of Africa and a lack of sufficient
water for construction in others, add to overall cost. Nevertheless, rainwater
collection is becoming more widespread in Africa with projects currently in
Botswana, Togo, Mali, Malawi, South Africa, Namibia, Zimbabwe, Mozambique, Sierra
Leone and Tanzania among others. Kenya is leading the way. Since the late 1970s,
many projects have emerged in different parts of Kenya, each with their own
designs and implementation strategies. These projects, in combination with the
efforts of local builders called “fundis” operating privately and
using their own indigenous designs, have been responsible for the construction
of many tens of thousands of rainwater tanks throughout the country. Where cheap,
abundant, locally available building materials and appropriate construction
skills and experience are absent; ferro-cement tanks have been used for both
surface and sub-surface catchment.
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Rainwater tanks constructed by local builders called
"fundis" in Kenya.
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Dar es
Salaam, Tanzania
Due to inadequate piped water supplies, the University of Dar es Salaam has
applied rainwater harvesting and utilisation technology to supplement the piped
water supply in some of the newly built staff housing. Rainwater is collected
from the hipped roof made with corrugated iron sheets and led into two “foul”
tanks, each with a 70-litre capacity. After the first rain is flushed out, the
foul tanks are filled up with rainwater. As the foul tanks fill up, settled
water in the foul tanks flows to two underground storage tanks with a total
capacity of 80,000 litres. Then, the water is pumped to a distribution tank
with 400 litres capacity that is connected to the plumbing system of the house.
The principles for the operation of this system are: (i) only one underground
tank should be filled at a time; (ii) while one tank is being filled, water
can be consumed from the other tank, (iii) rainwater should not be mixed with
tap water; (iv) underground storage tanks must be cleaned thoroughly when they
are empty; (v) in order to conserve water, water should only be used from one
distribution tank per day.
Botswana
Thousands of roof catchment and tank systems have been constructed at a number
of primary schools, health clinics and government houses throughout Botswana
by the town and district councils under the Ministry of Local Government, Land
and Housing (MLGLH). The original tanks were prefabricated galvanized steel
tanks and brick tanks. The galvanized steel tanks have not performed well, with
a short life of approximately 5 years. The brick tanks are unpopular, due to
leakage caused by cracks, and high installation costs. In the early 1980s, the
MLGLH replaced these tanks in some areas with 10-20 m3 ferro-cement tanks promoted
by the Botswana Technology Centre. The experience with ferro-cement tanks in
Botswana is mixed; some have performed very well, but some have leaked, possibly
due to poor quality control.
Brazil
Over the past decade, many NGOs and grassroots organisations have focused their
work on the supply of drinking water using rainwater harvesting, and the irrigation
of small-scale agriculture using sub-surface impoundments. In the semi-arid
tropics of the north-eastern part of Brazil, annual rainfall varies widely from
200 to 1,000 mm, with an uneven regional and seasonal rainfall pattern. People
have traditionally utilised rainwater collected in hand-dug rock catchments
and river bedrock catchments.
To address the problem of unreliable rural drinking water supply in north-eastern
Brazil, a group of NGOs combined their efforts with government to initiate a
project involving the construction of one million rainwater tanks over a five
year period, with benefits to 5 million people. Most of these tanks are made
of pre-cast concrete plates or wire mesh concrete.
Rainwater harvesting and utilisation is now an integrated part of educational
programs for sustainable living in the semi-arid regions of Brazil. The rainwater
utilisation concept is also spreading to other parts of Brazil, especially urban
areas. A further example of the growing interest in rainwater harvesting and
utilisation is the establishment of the Brazilian Rainwater Catchment Systems
Association, which was founded in 1999 and held its 3rd Brazilian Rainwater
Utilisation Symposium in the fall of 2001.
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| A tank made of pre-cast concrete plates. |
A tank made of wire mesh concrete. |
Bermuda
The island of Bermuda is located 917 km east of the North American coast.
The island is 30 km long, with a width ranging from 1.5 to 3 km. The total area
is 53.1 km2. The elevation of most of the land mass is less than 30 m above
sea level, rising to a maximum of less than 100 m. The average annual rainfall
is 1,470 mm. A unique feature of Bermuda roofs is the wedge-shaped limestone
“glides” which have been laid to form sloping gutters, diverting rainwater
into vertical leaders and then into storage tanks. Most systems use rainwater
storage tanks under buildings with electric pumps to supply piped indoor water.
Storage tanks have reinforced concrete floors and roofs, and the walls are constructed
of mortar-filled concrete blocks with an interior mortar application approximately
1.5 cm thick. Rainwater utilisation systems in Bermuda are regulated by a Public
Health Act which requires that catchments be whitewashed by white latex paint;
the paint must be free from metals that might leach into water supplies. Owners
must also keep catchments, tanks, gutters, pipes, vents, and screens in good
repair. Roofs are commonly repainted every two to three years and storage tanks
must be cleaned at least once every six years.
St. Thomas,
US Virgin Islands
St. Thomas, US Virgin Islands, is an island city which is 4.8 km wide and 19
km long. It is situated adjacent to a ridge of mountains which rise to 457 m
above sea level. Annual rainfall is in the range of 1,020 to 1,520 mm. A rainwater
utilisation system is a mandatory requirement for a residential building permit
in St. Thomas. A single-family house must have a catchment area of 112 m2 and
a storage tank with 45 m3 capacity. There are no restrictions on the types of
rooftop and water collection system construction materials. Many of the homes
on St. Thomas are constructed so that at least part of the roof collects rainwater
and transports it to storage tanks located within or below the house. Water
quality test of samples collected from the rainwater utilisation systems in
St. Thomas found that contamination from faecal coliform and Hg concentration
was higher than EPA water quality standards, which limits the use of this water
to non-potable applications unless adequate treatment is provided.
Island
of Hawaii, USA
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| A wooden water tank in Hawaii, USA |
At the U.S. National Volcano Park, on the Island of Hawaii, rainwater utilisation
systems have been built to supply water for 1,000 workers and residents
of the park and 10,000 visitors per day. The Park’s rainwater utilisation
system includes the rooftop of a building with an area of 0.4 hectares,
a ground catchment area of more than two hectares, storage tanks with two
reinforced concrete water tanks with 3,800 m3 capacity each, and 18 redwood
water tanks with 95 m3 capacity each. Several smaller buildings have their
own rainwater utilisation systems as well. A water treatment and pumping
plant was built to provide users with good quality water. |
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