U.S. website whatsinmywater.com warns people they need to be concerned about what is getting into their tap water. It cites the EPA as reporting that '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'.
The site also says 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).
Whatsinmywater.com notes how 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…”