A water quality study done in Sonoma County, CA by UC Berkeley showed that the elderly tend to be less tolerant to contaminants in drinking water. Sonoma County was targeted by the study because it meets all the Federal standards for water quality. Basically the water is "safe" to drink by government standards.
The study shows that the older residents were 12% more likely to experience more severe gastrointestinal illnesses. While 12% may not seem like much it is statistically significant because it lies outside the range of normal deviation. So while Federal standards are "safe" for most users, there is still a risk to people with weaker immune systems because trace levels of contaminants remain in drinking water.
Water filters are a practical way to solve the problem. You can take control of your drinking water quality by using a simple carbon filter, which will remove most particulate matter as well as chlorine taste and odor from your water.