In the US, tap water is regulated to higher standards than bottled! In the rare cases where there is a problem with it, everyone gets notified, for example http://www.msdh.state.ms.us/msdhsite/_static/23,0,148.html.
NYC prides itself on having really good water, both for local food production, and just for taste. NYC did this by buying up land around its reservoirs further inland and building a large aqueduct system. The water isn't even filtered!
That said, some locations have unpalatable water, such as towns near the ocean that get their water from nearby wells.