Tap water is cheap, democratic (in that water authorities provide a public good) and remarkably safe. It doesn't take enormous amounts of oil to be bottled and shipped. Apart from the rare, unavailable bottle -- mostly when I'm hot and exhausted in tourist areas of D.C. and there's no fountain, or when I'm visiting someone's home -- I drink tap water. (Under the same rubric, I've even cut back on soft drinks, preferring home- or office-brewed coffee or tea.) Bad bits of news about the United States water supply won't dissuade me.
Unconvinced? need some facts? I'll defer to today's article at Treehugger.