Rainwater harvesting
Practical Action
Storage tanks and cisterns
The water storage tank usually represents the biggest capital investment element of a
domestic RWH system. It therefore requires careful design to provide optimal storage
capacity while keeping the cost as low as possible. The catchment area is usually the existing
rooftop or occasionally a cleaned area of ground, as seen in the courtyard collection systems
in China. The guttering for the system can often be obtained relatively cheaply, or can be
manufactured locally.
There are an almost unlimited number of options for storing water. Common vessels used for
very small-scale water storage in developing countries include plastic bowls and buckets,
jerrycans, clay or ceramic jars, cement jars, old oil drums, empty food containers, etc. For
storing larger quantities of water, the system will require a tank or a cistern. For the purpose
of this document, we will classify the tank as an above-ground storage vessel and the cistern
as a below-ground storage vessel. These can vary in size from a cubic metre or so (1000
litres) up to hundreds of cubic metres for large projects. The typical maximum size for a
domestic system is 20 or 30 cubic metres. The choice of system will depend on a number of
technical and economic
considerations listed below.
Space availability
Options available locally
Local traditions for
water storage
Cost of purchasing new
tank
Cost of materials and
labour for construction
Materials and skills
available locally
Ground conditions
Use of RWH – whether
Figure 3b: Cutting plastic pipe into half to make gutter
the system will provide
total or partial water
supply
One of the main choices will be whether to use a tank or a cistern. Both tanks and cisterns
have their advantages and disadvantages. Table 1 summarises the pros and cons of each:
Pros
Cons
Tank
Above ground structure allows easy
inspection for leakages
Many existing designs to choose from
Can be easily purchased ‘off-the-shelf’
Can be manufactured from a wide
variety of materials
Easy to construct from traditional
materials
Water extraction can be by gravity in
many cases
Can be raised above ground level to
increase water pressure
Require space
Generally more expensive
More easily damaged
Cistern
Generally cheaper due to lower
material requirements
Not vulnerable to water loss by tap left
open
Require little or no space above
ground
Unobtrusive
Surrounding ground gives support
allowing lower wall thickness, and
thus lower costs
Water extraction is more problematic,
often requiring a pump
Leaks are more difficult to detect
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