An underground tank (or sub-surface tank), is a water storage structure constructed below the ground. The term also includes structures that are partially below ground. In most cases,underground tanks collect and store runoff from ground catchments such as open grasslands,hillsides, home compounds, roads, footpaths, paved and unpaved areas.However, in certain circumstances, roof catchments can also be channeled into underground tanks.
Underground tanks are especially suited to homesteads having thatched roofs and other structures or for areas where a roof catchment may not be feasible. However, it may be necessary to pump (lift) water, except where the ground gradient permits and where gravity outlets are constructed. Underground tanks can be designed as spherical or cylindrical and constructed using bricks. Since underground tanks get support from the surrounding ground, thus they can be built with less reinforcing material. Thus, underground tanks have lower construction costs and therefore, are more suited for storing agricultural water than surface tanks.
Advantages of sub-surface tanks:
- Underground tanks offer a cheaper to install due to its lower cost of reinforcements neededduring construction, as compared to surface tanks. This is due because ground support provides the strength needed to hold the water
- They are appropriate in places where space above ground is limited; and they can be made larger than surface tanks
- The water is sometimes cooler
- Larger volumes of water can be stored.