Unless issued by your local health department, avoid “free home water testing” offers—they are normally a come-on to get you to buy water treatment devices after a couple of carefully staged tests. The only way to be sure that your water has certain harmful pollutants is to have it tested by an independent lab.

Unfortunately, you must test for each type of pollutant separately, which can be very expensive. If you get your water from a municipal utility, quality can change daily, so most tests are worthless—and usually unnecessary. Still, it may be a good idea to check for lead because lead can leach into the water from old lead-based plumbing.

You can also discover plenty of information without testing. Call your health department or water supplier and request copies of water treatment reports and note any violations. Look for the frequency and scope of the tests. Ask whether your area is known for any special hazards, especially those that might enter water between the treatment plant and your tap.

Why we like it: • Removes chlorine, polishes taste • Switches easily from non-filtered to filtered • Removes most bacteria, lead, and sediment

If you have a well, at the very least check it once for mineral content, lead, and radon (where radon is a threat) and once or twice a year for bacteria and nitrate. If you have concerns about contaminants in well water, contact your local health department for recommendations. They may handle certain tests, such as bacterial testing.

A partial chemical test that will detect magnesium, calcium, sodium, iron, fluoride, chloride, and nitrate is usually relatively affordable. To look for chemicals such as solvents, pesticides, and petroleum products can be very expensive because each requires its own test.

Find an independent testing lab by asking your water utility or the state health department for a recommendation, or looki under “Laboratories” in the telephone directory or online. You can also contact one of the mail-order laboratories that specialize in water analysis at an affordable price, such as National Testing Labs (800-458-3330) or Suburban Water Testing (800-433-6595). They will send you the proper supplies and instructions for collecting a sample, which you mail back. A lead-only test costs about $35; a comprehensive test for bacteria, organics, and inorganics runs from $119 to $145.