Underground rainwater harvesting
Once the tank is installed, rainwater is cheaper to collect than water conveyed from
expensive storage facilities such as dams, which are usually located far away from the
Using rainwater tanks regularly may reduce storm water run-off from your field. This may
reduce flooding, erosion and environmental damage to streams.
Rainwater tanks provide a secondary backup water supply to your crops should there be a
failure or erratic rains or long dry spells.
Some disadvantages of using underground rainwater tanks
It is difficult to detect the leaks and take corrective measures in case of under ground
Water from under ground tanks cannot be drawn by gravity. Some kind of manual or
power lifting devices need to be used for drawing the water.
Further, in coastal areas, under ground tanks are prone to water contamination due to
fluctuation in groundwater table and leakage of stored water.
A rainwater tank may be costly to purchase and install and will require some
maintenance. If rainwater from the tank is supplied using a pump then this will need to
be maintained and occasionally repaired or replaced.
If a small tank, less than 10 000 litres is used to store rainwater, it will probably empty
frequently, particularly during summer. (However, it is possible to arrange your system so
that you have rainwater available for drinking all year round.)
Rainwater tank maintenance
Ongoing planned maintenance will maintain your rainwater quality and extend the life of your
system. Maintenance should include the following:
Regularly check the tank to ensure there are no unscreened or damaged openings that
allow insects, rodents or animals to get into the tank.
Check gutters and strainers devices at least twice before and after the rainy season. Keep
them clean and free of leaves and debris. Ensure the tank lid is tight.
Check the tank every two years for sludge and have the tank cleaned if there is a thick
layer of sludge on the bottom of the tank.
Lang, J., Allen, M and van der Wel, B. (2002). Good Alternative Rainwater Tanks: Fact
or Fiction? 2002 Water Symposium Proceedings. Office of Sustainability, Department
for Environment and Heritage.
Nissen-Petersen, E., (1992) How to Build an Underground Tank with Dome, ASAC
Consultants Ltd., Kitui, Kenya, 1992.
Runoff Rainwater Harvesting Practical Action Technical Brief
The Sri Lankan ‘Pumpkin’ Tank ~ Case Study Practical Action Technical Brief
The Underground Brick Dome Water Tank ~ Case Study Practical Action Technical Brief
Cement Mortar Jar ~ Case Study Practical Action Technical Brief
Rainwater Catchment Systems for Domestic Supply, by John Gould and Erik Nissen-
Petersen, Practical Action Publishing 1999.
Ferrocement Water tanks and their Construction, S. B. Watt. Practical Action Publishing
Rainwater Harvesting: The Collection of Rainfall and Runoff in Rural Areas, Arnold Pacey
and Adrian Cullis Practical Action Publishing 1986
Water Harvesting – A Guide for Planners and Project Managers, Lee, Michael D. and
Visscher, Jan Teun, IRC International Water and Sanitation Centre, 1992
Water Harvesting in five African Countries, Lee, Michael D. and Visscher, Jan Teun, IRC /
UNICEF, 1990. As snapshot of the status of RWH in five African countries.
Waterlines Journal Vol. 18, No 3, January 2000 and Vol. 14, No.2, October 1995 Both
issues are dedicated to rainwater harvesting, available through Practical Action