Rivalries over water have been the source of disputes since humans settled down to cultivate food.
Even our language reflects these ancient roots: "rivalry" comes from the Latin rivalis, or "one using the same river as another".
"The scramble for water has begun, and governments must react; the implications of doing nothing are too profound to contemplate. Dominic Waughray, Senior director, head of environmental initiatives, World Economic Forum, Geneva
Some BBC links about water
http://news.bbc.co.uk/1/hi/sci/tech/7886646.stm