Newsletter and Technical Publications
Rainwater Harvesting And Utilisation
An Environmentally Sound Approach for Sustainable
Water Management: An Introductory Guide for Decision-Makers
General Description of the Technology
Development of Rainwater Harvesting and Utilisation
Rainwater harvesting and utilisation systems have been used since ancient times
and evidence of roof catchment systems date back to early Roman times. Roman villas
and even whole cities were designed to take advantage of rainwater as the principal
water source for drinking and domestic purposes since at least 2000 B.C. In the
Negev desert in Israel, tanks for storing runoff from hillsides for both domestic
and agricultural purposes have allowed habitation and cultivation in areas with
as little as 100mm of rain per year. The earliest known evidence of the use of
the technology in Africa comes from northern Egypt, where tanks ranging from 200-2000m3
have been used for at least 2000 years many are still operational today.
The technology also has a long history in Asia, where rainwater collection practices
have been traced back almost 2000 years in Thailand. The small-scale collection
of rainwater from the eaves of roofs or via simple gutters into traditional jars
and pots has been practiced in Africa and Asia for thousands of years. In many
remote rural areas, this is still the method used today. The world's largest rainwater
tank is probably the Yerebatan Sarayi in Istanbul, Turkey. This was constructed
during the rule of Caesar Justinian (A.D. 527-565). It measures 140m by 70m and
has a capacity of 80,000 cubic metres.
of Rainwater Harvesting Systems
Typically, a rainwater harvesting
system consists of three basic elements: the collection system, the conveyance
system, and the storage system. Collection systems can vary from simple types
within a household to bigger systems where a large catchment area contributes
to an impounding reservoir from which water is either gravitated or pumped to
water treatment plants. The categorisation of rainwater harvesting systems depends
on factors like the size and nature of the catchment areas and whether the systems
are in urban or rural settings. Some of the systems are described below.
(i) Simple roof water collection systems
While the collection of rainwater
by a single household may not be significant, the impact ofthousands or even
millions of household rainwater storage tanks can potentially be enormous. The
main components in a simple roof water collection system are the cistern itself,
the piping that leads to the cistern and the appurtenances within the cistern.
The materials and the degree of sophistication of the whole system largely depend
on the initial capital investment. Some cost effective systems involve cisterns
made with ferro-cement, etc. In some cases, the harvested rainwater may be filtered.
In other cases, the rainwater may be disinfected.
Example of a roof catchment system.
(ii) Larger systems for educational institutions, stadiums, airports, and
When the systems are larger, the overall system can become
a bit more complicated, for example rainwater collection from the roofs and
grounds of institutions, storage in underground reservoirs, treatment and then
use for non-potable applications.
(iii) Roof water collection systems for high-rise buildings in urbanised
In high-rise buildings, roofs can be designed for catchment purposes
and the collected roof water can be kept in separate cisterns on the roofs for
At Kokugikan sumo wrestling arena in Tokyo, Japan,
rainwater collected from the arena's 8,400 square meter rooftop is used
for non-potable purpose.
(iv) Land surface catchments
Rainwater harvesting using ground or land
surface catchment areas can be a simple way of collecting rainwater. Compared
to rooftop catchment techniques, ground catchment techniques provide more opportunity
for collecting water from a larger surface area. By retaining the flows (including
flood flows) of small creeks and streams in small storage reservoirs (on surface
or underground) created by low cost (e.g., earthen) dams, this technology can
meet water demands during dry periods. There is a possibility of high rates
of water loss due to infiltration into the ground, and because of the often
marginal quality of the water collected, this technique is mainly suitable for
storing water for agricultural purposes.
Example of a ground catchment system.
(v) Collection of stormwater in urbanised catchments
The surface runoff
collected in stormwater ponds/reservoirs from urban areas is subject to a wide
variety of contaminants. Keeping these catchments clean is of primary importance,
and hence the cost of water pollution control can be considerable.