Rainwater harvesting
Practical Action
of an integrated water supply system. It is a technology that is flexible and adaptable to a very
wide variety of conditions. RWH is used in the richest and the poorest societies on our planet,
and in the wettest and the driest regions of the world.
Components of a domestic RWH system
Domestic RWH systems (DRWH) vary in complexity. Some of the traditional Sri Lankan
systems are no more than a pot situated under a piece of cloth or a plastic sheet tied to four
poles. The cloth captures the water and diverts it through a hole in its centre into the pot. In
contrast, some of the sophisticated systems manufactured in Germany incorporate clever
computer management systems, submersible pumps, and links to grey water and domestic
plumbing system mains. Somewhere between these two extremes, we find the typical DRWH
system in use in developing countries. Such a system will usually comprise a collection
surface (a clean roof or ground area), a storage tank, and guttering to transport the water from
the roof to the storage tank. Other peripheral equipment is sometimes incorporated, for
example: first-flush systems to divert the dirty water which contains roof debris after
prolonged dry periods; filtration equipment and settling chambers to remove debris and
contaminants before water enters the storage tank or cistern; handpumps for water extraction;
water level indicators, etc.
Typical domestic RWH systems
A typical domestic RWH consists of a collection surface, gutters and a storage container. In
addition, there are options for diverting first-flush water and filtration.
Collection surfaces
For domestic rainwater harvesting
the most common surface for
collection is the roof of the
dwelling. Many other surfaces can
be, and are, used: courtyards,
threshing areas, paved walking
areas, plastic sheeting, trees, etc.
In some cases, as in Gibraltar, large
rock surfaces are used to collect
water which is then stored in large
tanks at the base of the rock slopes.
The style, construction and material
Figure 1: A typical corrugated iron sheet roof,
showing guttering. Photo: Practical Action
of the roof affect its suitability as a
collection surface for water. Typical
materials for roofing include
corrugated iron sheet (also known
as tin roof), asbestos sheet; tiles (a wide variety is found), slate, and thatch (from a variety of
organic materials). Most thatch are suitable for collection of rainwater, but only certain types
of grasses e.g. coconut and anahaw palm (Gould and Nissen Peterson, 1999), thatched
tightly, provide a surface adequate for high quality water collection. The rapid move towards
the use of corrugated iron sheets in many developing countries favours the promotion of
RWH.
Guttering
Guttering is used to transport rainwater from the roof to the storage vessel. Guttering comes
in a wide variety of shapes and forms, ranging from the factory made PVC type to home-made
guttering using bamboo or folded metal sheet (Figure 1). Guttering is usually fixed to the
building just below the roof and catches the water as it falls from the roof.
Some common types of guttering and fixings are shown in Figure 2:
2