Underground rainwater harvesting
Practical Action
5. Construction costs
To save costs use as many available local materials as possible as shown below. Work in
groups to share labour, as this is a labour intensive system. It takes approximately fours for
ten people to construct a 10 000litre tank.
Materials required
1 rammer locally made from dry wood, Ant-hill soil (termitaria), water, 5 x 1,5-2m long dry
poles, Pick, shovel (depending on labour available), 10 farm/earth bricks, Tape measure or
ruler, string 2m, knife/hacksaw/small axe, 50 wooden pegs, old Hessian or plastic bags. 25kg
cement.
Constructing the underground tank
1. Along any dug dead level contour (which is your collection area) choose where you can
construct your storage tank. All soils that allow rapid percolation the closer should be the
storage tanks. This because your soil quickly loses water and that’s where your plants are
likely to show signs of moisture stress during the dry spell.
2. Measure along the channel the length of the tank you want and mark using pegs.
Dig the marked area up to a further depth of 500cm or more. The deeper it is the more
water will be harvested.
Picture 1: Foundation of the
underground tank ©Practical
Action/Douglas Gumbo
3. Mark with a shovel the root zone depth within your tank.
4. Place termitaria-cement mixture at the base of the tank and sprinkle water to facilitating
easy ramming.
5. Using homemade rammer, start ramming up to a maximum depth of 2-5cm. Sprinkle
whenever required.
6. All the tanks must have a non-permeable layer therefore a thicker layer may be required
to avoid seepage and deep percolation. Picture 2 below the process of ramming.
7. Mix termitaria with water to make mortar and plaster up to the marked root zone level of
your deep-rooted crops as shown in Picture 3.
The table below indicates the recommended options for your tank lining when plastering the
walls.
Material use
Cement-anthill/termitaria
Cement-clay soil
Cement-sand soil
Cement –soil ratio
1:8
1:8
1:3
Thickness (mm)
50
60
50
2