Many people drink tap water because it is cheap, plentiful and perceived to be safe. A recent investigative report at Associated Press shows that many pharmaceutical drugs can end up in the water supply. Bottled water is not safer because it is either packaged tap water or untested and unregulated groundwater that can also be contaminated. Great coverage of this can be found on Democracy Now! which aired an interview with one of the AP reporters.
I do understand how these drugs are ending up in the water supply. So many things are prescribed and available on the shelves that that it is inevitable. We are excreting it and some people are flushing unused drugs down the toilet. No regulations exist and the problem was not widely known until this report. I am unclear as to how this affects those of us who drink the water, what can be done to treat waste and the water coming in and how these drugs react with each other in the environment and when they get into our bodies.
Hopefully people take action and start finding available services to properly dispose of extra drugs or reduce their need for them in the first place. Replace cholesterol drugs with fewer bacon cheeseburgers for example. We'll see what happens.