Attacking the water supply is a common tactic throughout history. It is the current tactic the United States military is using to subdue the rebellion in Baghdad.
Baghdad, a city of 4.5 million people, has no running water. Some parts of the city have been without water for six days. The temperature today was 117 degrees F. The official excuse is power shortages but I have no doubt it fits nicely into the Surge. It is difficult to wage war when your children are dying of dehydration.
The reason I believe this is a deliberate American tactic is that we have done it before. In 2004, the Marines cut off water and electrical supplies to Tal Afar, Sammara, and Fallujah as part of their offensive against Sunnis in that region. The resulting deprivation killed thousands.
While imposing such suffering on the people of Baghdad may lead to short-term success it cannot bring about victory unless we are willing to bring it all the way to genocide. Oh, by the way, depriving the civilian population of water is considered a war crime by the Geneva Convention.