What to Look For

In many U.S. cities, the drinking water is perfectly safe, and across the country, municipal supplies are tested daily for some contaminants, weekly and monthly for others. But after hearing reports of pesticides, pharmaceuticals and other industrial contaminants in water supplies, people often turn to water filters for added peace of mind.

The best way to ensure clean and safe drinking water is to protect our watersheds, which act as natural filters absorbing chemicals, pollutants and sediments. In the meantime, a temporary solution is to filter the water in your home.

Always select filters certified by the National Sanitation Foundation (NSF), which tests products to ensure that they remove what the manufacturers say they do. NSF has an extensive searchable database on their website, www.nsf.org/Certified/dwtu/.

No filter will remove every contaminant of concern, but here are the most common types and the major contaminants they can handle.

Carbon-filter models include carafes (pitchers), faucet-mounted models, undersink models (usually require a permanent connection to an existing pipe) and whole-house or point-of-entry systems (usually installed in the basement or outside). Carbon, a porous material, absorbs impurities as the water passes through.

What they remove: lead, PCBs, chlorine byproducts (chloramines and trihalomethanes), certain parasites, radon, pesticides and herbicides, the gasoline additive MTBE, the dry-cleaning solvent trichloroethylene, some volatile organic compounds, some levels of bacteria (such as Cryptosporidium and Giardia) and a small number of pharmaceuticals.

Reverse-osmosis systems push water through a semi-permeable membrane, which acts as an extremely fine filter, and they're often used in conjunction with carbon filters. However, they waste four to nine gallons of water for every gallon filtered.

What they remove: perchlorate, sulfates, fluoride, industrial chemicals, heavy metals (including lead), chlorine byproducts, chlorides (which make water taste salty) and pharmaceuticals.

Ultraviolet light disinfects water, killing bacteria. Countertop units can be found for under $100, but most whole-house units cost $700 and up for NSF-certified models.

What they remove: bacteria; use with carbon filter to remove other contaminants.

Distillers, probably the least practical home method, boil and condense water. While countertop units are available, distillers use lots of electricity, generate excess heat and require regular cleaning. Explore filters or other alternatives to remove your contaminant, or, in a pinch, buy distilled water.

What they remove: heavy metals (including lead), particles, total dissolved solids, microbes, fluoride, lead and mercury.

Shopping Tips

• Your water may not need to be filtered at all. Read your water utility's annual consumer confidence or "right to know" report, which you can get from your utility or online at www.epa.gov/safewater/dwinfo.htm, to find out if your water has contaminants. These can be difficult to interpret, so download a guide to reading them at www.safe-drinking-water.org/rtk.html

Usage Tips

• Change the filter cartridge as recommended by the manufacturer. Improper maintenance allows bacteria and other contaminants to build up.

• Lead can enter your water through old pipes. Pregnant women and parents of young children should have their water tested for lead. Tests run from free to $15. For a list of state-certified lead-testing labs, see www.epa.gov/safewater/faq/sco.html or contact your county health department.

• If your water comes from a private well, the EPA recommends that you have it tested annually by a state-certified lab for nitrate and coliform bacteria, more often if you live near farms or factories. For more information, see www.wellcarehotline.org or call your local health department.