Depletion and contamination of water sources

As you read in Study Session 1, humans interact with water both by using it and by producing the wastes that may contaminate it. Both of these activities can damage water sources.

Water source depletion

Although water is a renewable resource, excessive extraction of water will result in its depletion. If groundwater is extracted from aquifers more quickly than the water is replenished by recharging, this will lower the water table. Excessive groundwater pumping changes the flow patterns around wells and creates a localised depletion of groundwater stores in the area around the well. If several wells are located close together these zones can overlap. The result is that existing wells and boreholes may dry up and new ones have to be dug deeper and deeper before they reach water. The lowering of the water table also affects rivers and streams, which are normally fed partially by underground water. Over-exploitation of groundwater can also affect springs, which may change from permanent to temporary or even dry up completely.

Water source depletion is also directly linked to reduction in forest cover. With the loss of trees and other vegetation, rainwater runs straight off the surface and does not penetrate into the ground to recharge the groundwater. Added to this are the uncertainty of climate change and the effects of periods of drought which have a serious impact on the availability of surface and groundwater sources.

Water source contamination

Surface water can become contaminated in many ways. This may by direct discharge into the river from a sewer or pipe. Rivers and streams are considered to be convenient ways of disposing of wastewaters of all types, including domestic and industrial wastes. Industrial sources may discharge hazardous substances, as well as organic matter and suspended solids without adequate treatment. Surface water pollution can also come from stormwater run-off, which may carry contaminated materials into the water. Open defecation and the uncontrolled disposal of solid wastes are two likely sources of contamination by run-off.

Groundwater is generally cleaner than surface water for reasons explained earlier but pollution of groundwater resources has become a major problem around the world. Groundwater is polluted by the leaching of human and industrial waste, pesticides and fertilisers, which infiltrate into the aquifers from the surface and pollute groundwater supplies. Pit latrines that are located too close to a water source or are poorly constructed and maintained can also be sources of groundwater contamination. The polluted water reaches people and animals through contaminated spring and well water.