Ample clean water is essential to life, especially a healthy one. Putting something so critical to our existence into the hands of profiteers is suicidal to mankind, or at the very least, will result in serious quality of life issues as we try to decide which is most important...the water bill, the grocery bill, or the fuel bill.
The only place I can support water privatization would be in certain remote or impoverished regions where the government is either non-existent or so broke that any reliable water supply would be better than what they currently have. But no private company would bother with those areas anyway.
Watch the eye-opening documentary, "Flow", for a look at what happens when corporations buy up our water for profit.