Natural resources: Water resources

Water resources
Almost 71% of earth's surface is covered by water of which 97% is ocean waterwhich is unusable due to high salt concentration. Almost 2.6% of fresh water is  is trapped in ice caps and glaciers along with some part stored underground. Only 0.4% of the total quantity of water is available in swamps, rivers, lakes and streams.

Surface water sources
Sea water
River and streams
Natural lakes and ponds
Artificial impounding reservoirs

Ground water sources
After glaciers, ice caps and snow fields, ground water is the next largest fresh water reservoir. Precipitation that does not run-off over the surface, percolates through the soil and either accumulates in an underground basin or flows underground in sub surface streams.

Effects of over-utilizing ground water
-Excessive pumping of ground water causes porous formations to collapse resulting in subsidence
-Heavy pumping can lower water table and cause shallow wells to dry-up or even deplete the entire aquifer.
-Over-use of freshwater reservoirs along coast lines often allows salt water to intrude into aquifers rendering the water unfit for domestic, industrial or agricultural purposes.