4 TIPS FOR WATER HARVESTING IN AFRICA

Most African farmers rely on seasonal rainfall for their agricultural production. This means that production goes down drastically during the dry months. Smallholder farmers who cannot afford sophisticated irrigation systems or who do not have access to a water source would be well advised to look into water harvesting and irrigation.  Here are a few simple ideas:

• Use Rooftop Catchments

By installing gutters along their roofs, farmers can easily harvest rain water and then use it during dry spells. Harvesting water from a roof works best if the roof is made of corrugated iron sheets, galvanized iron or reinforced cement concrete.  Tiled roofs can also be used to harvest rain water. Avoid roofs that are painted with metallic paint because these can change the chemical composition of the water.

The rooftop and the gutters attached together form the catchment. They receive the water that is used in the water harvesting system.

The gutters must always be well supported to ensure that they do not fall off when loaded with water. If they cannot be fixed to the walls, let them be firmly attached. Gutters need to be made of locally available materials and should be big enough to accommodate the highest amount of rain. Should you use galvanized iron sheet, ensure that it is 20 to 22 gauge. Alternatively, use semicircular PVC gutters. Just cut the pipe into two semi circular parts. Some people use bamboo trunks to trap water.

Install a coarse mesh at the roof to ensure that the water passing into the gutter is not full of stones and debris.

• Use Land Surface Catchments

Alternatively, African farmers can use land surface catchments which are much simpler. Land surface catchments provide a potentially much larger surface for collecting rain water than rooftop catchments. They typically collect surface runoff and channel it to an underground storage reservoir. Land typically collects more water when it has less vegetation, a steeper slope and has more compact soil.

• Install Conduits

Conduits are channels that direct water to the storage area. PVC is the best material for water harvesting, although farmers can use any other locally available material such as galvanized iron. The diameter of the pipe should be calculated based on the rainfall intensity and the area of the roof. You could install simple filtration systems to keep the water tanks from filling up with sand.

• Install a Reservoir

The harvested rainwater must go into a reservoir where it is stored until it is needed for use. Reservoirs for water harvesting can be water tanks placed underground. They can also be water pans. Some farmers dig trapezoidal bunds which hold water for crop production. This is a very labor intensive method because it involves a lot of digging.

A pond can also serve as a reservoir. Simply dig a up a large enough pond and line the pond with waterproof material like polythene. Finally, dig furrows that will harness the rainwater and channel it to the pond.

The water in the pond can be pumped using an ordinary manual water pump. Farmers who can invest a little more money can buy electric pumps. For small holders, manual water pumps are often good enough.