Patty is right on, the problem with the water supply is that many farmers irrigate with water from underground aquifers that take centuries or more to fill up so when its gone it will take a long time to come back. In that situation they are not paying the actual cost. Also look at places where rivers have been diverted and overused upstream. (in Russia or the Rio Grande) . Canada has 1/4 of the worlds fresh water supply and even though water is not part of the free trade agreement there already is a company suing the Can. Govt for the right to export water.