Most people are under a very big misconception that the government or their city would never allow water that wasn't safe be pumped to their home.  But consider the following data released by the EPA:

It get's worse. EPA reports there were over 8,500 Health Based Violations for contaminants reported by Water Supply Systems last year for contaminants that exceeded the "higher" MLC level.

This is how serious the EPA considers those violations to be:
“A health-based violation means that either a system has exposed their users to what EPA has judged as an unreasonable risk of illness, or a system has failed to treat their water to the extent EPA has judged necessary to protect their users from an unreasonable risk of illness in the event that the regulated contaminant is present in source water”
(the above is from the EPA Safe Drinking Water Hotline Report)

The EPA even warns people about increased risk of drinking water contaminants by certain groups of people:
“Some people may be more vulnerable to contaminants in drinking water than the general population. Children and infants, pregnant women and their fetuses, the frail elderly, people undergoing chemotherapy or living with HIV/AIDS, and transplant patients can be particularly at risk for infections… If you have special health care needs, consider taking additional precautions with your drinking water…”
(EPA – Water On Tap: What you need to know - report)

However the possible dangers for contaminated water goes beyond what has been pumped from the ground by the Water Supply companies.. After the water is pumped from a well, lake or resevoir, it is put through a filtration process which basically consist of sand and gravel and then filtered water goes into a water tower or tank. But reports have been coming in from around the country about contaminants entering the filtered water in the water towers : Unfortunately most people believe because they live in a specific town and know the people who work for the village that everything is fine. But, those employees of the village do not always know about the problems lurking in their towns water tower.
"The Environmental Protection Agency is taking notice. During a conference last month, the EPA shared pictures of water towers with improper hatches and vents, allowing mice, snakes, birds and even feces into the water. And in North Texas, “we see wasps, geckos, lizards” in water towers, one of Perrin’s divers told CBS 11 News."    www.epa.gov/safewater/disinfection/tcr/pdfs/whitepaper_tcr_storage.pdf)