The place to start is your local public water utility. If you're a homeowner, you can find its address and phone number on your bill. If you rent, check the phone book.
Many utilities also have Web sites.
You should also ask for a printout of the levels of all 80 contaminants, since the EPA's limits for arsenic and disinfection byproducts are too high. If you get your water from a well, you'll need to get it tested yourself. Call the EPA Safe Drinking Water Hotline for information on how to obtain a list of certified labs. They're the most common disinfection byproducts. Keep in mind that outbreaks of gastrointestinal illness have occurred at levels as low as 0.2 NTU, which aren't enough to make the water look cloudy.