Last month, there was a news story about large city water processing systems. Many allow miniscule amounts of pharmaceuticle drugs, hormones and vitamins, passed through human waste, to reenter the drinking supply.
If you're concerned about this and in the market for a filtration system, there are many to choose from. One of the most effective is the Reverse Osmosis system, with pre- and post carbon filtration. Some models will mount to the plumbing beneath the kitchen sink. The (OS) system is effective in removing chemicals, metals, lead and many other pollutants and toxins that others won't.
In addition, it is important to have the water tested before actually looking for a water filter. Local water dept. may reslease a list of pollutants they find during testing. Also, a sample can be sent to a laboratory for testing, from $35.00 to $170.00, depending on what specific artifacts are being researched.