Water is abundant on this planet, and unlike nonrenewable resources
such as oil or gas, is constantly circulating through hydrological cycles.
Consequently, the total amount of water will change only when measured
in terms of geological time. Although abundant, 83% of the earth’s water
is present as salt water. Another 14% of the total is chemically bound and
thus unavailable for drinking. With another 2% of the total present as ice
and snow, only 0.5% is available as freshwater. Indeed, of the total avail-
able freshwater, almost 98% is present in underground aquifers, with less
than 2% present in lakes and rivers (de Moel et al., 2006)