69Aquifers occur when underground layers of water seep into permeable rock or
other materials such as sand, gravel, silt or clay. They generally occupy large areas
under the earth’s surface and will often supply water sources such as streams, rivers
and springs. Aquifers are often on the receiving end of water harvesting, in that they
can store harvested rainwater. Recently, awareness of depleting aquifers has spurred
an increase in WH techniques that aim to directly recharge these depleting resources.
Many forms of rainwater harvesting collect water and store it underground for
Fig. 13 An ancient groundwater harvesting system in Kathmandu, Nepal (Source: Akhtar Ali)
Fig. 14 Groundwater
harvesting well in Pakistan
(Source: Akhtar Ali)
Water Harvesting in Dry Environments