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Water shortage for human use are gradually being felt in various parts of the  earth. The crisis will get even worse as time marches on. Here is the summary  of a recent radio program (BBC or NPR I cannot remember) I heard on this subject and possible solutions.

The state of Nevada in the US is mostly dessert and the city of Les Vegas  (2 million residents and 14 million visitors/year) is located in the middle of  the dessert. In 1922 long before there was the city of LasVegas, Nevada and two other neighboring states, California,and Arizona,negotiated an agreement on how much water each state can take from Lake Mead which is a man made  lake by building a dam along the Colorado river.  Thus, the question “how does Las Vegas manage its meager allocation of water currently for her large  population of residents and visitors?” Here are the solutions:

1.  It turns out that 40% of water use in a city is waste water which  can be treated and reused. Thus for every gallon of water Las Vegas take out form Lake Mead they get 70% more to use (=1+0.4+(0.4)^2+(0.4)^3+ . . .)

2.  Plentyof solar power to utilize to run pumps and filters to recycle waste water.

3.  The Other 60% of the water are for outdoor  use and cannot  be recovered.  Thus cut back on outdoor use, e.g., swimming pool, lawn care, etc. via regulation.

4.  Encourage underground watering of lawn and plants to prevent  evaporation and waste.

By combination of items 1-4 Las Vegas has become a model of municipal  water management worldwide.