Although 70% of the earth’s surface is covered by water, more than 97% resides in the oceans as salt water that cannot be consumed. The remaining 2.5% exists as fresh water, but only one-third of this water is actually available since the remainder is trapped as ice in the polar caps and glaciers.
Fresh water is renewed by surface evaporation from all bodies of water returning to earth as rain. Underground aquifers, which contain 60 times the volume of surface water found in lakes and ponds, pro…