DO WATER FILTERS WORK?

By Christine Gorman

You've read about the outbreaks of waterborne illnesses in places like Milwaukee, Las Vegas, New York City and Washington. You've been concerned that traces of lead may be lurking in your pipes. So just to be on the safe side, you've installed a water filter on your kitchen tap. Trouble is, you may not be any better protected. In fact, the water you drink may be dirtier than it was before.

The U.S. is blessed with one of the best water-supply systems in the world. Yet half of all Americans worry about getting sick from tap water contaminants, according to a 1995 survey by the Water Quality Association. As if to underscore the point, the Environmental Protection Agency has ordered the nation's 300 largest municipal water suppliers to begin testing for the cryptosporidium parasite, which poses a risk for people with weakened immune systems.

No wonder American homeowners last year bought $450 million worth of water-treatment systems, up 30% from the $350 million they spent in 1994. According to Baytel Associates, a market-research firm in San Francisco, at least 12% of U.S. households treat the water in their homes in some fashion. Baytel expects that number to jump to 40% in the next 15 years.

But do these home treatment systems work? That depends, experts say, on what you want them to do. "Not every product does everything," says Nancy Culotta of Michigan's NSF International, an Ann Arbor-based industry watchdog group. Some filtering systems, she notes, merely improve the water's taste by getting rid of relatively harmless inorganic chemicals like sulfur or chlorine. Others do a creditable job of removing lead but aren't designed to purify water tainted by bacteria or other pathogens. And many of the most popular systems need to have their filters frequently replaced, or owners will wind up running their tap water through the high-tech equivalent of a dirty sponge.

Hundreds of products are on the market, but the technologies they use fall into a few basic categories:

ACTIVATED-CARBON FILTRATION. These systems are the most popular and the most effective in reducing so-called aesthetic contaminants like chlorine and sediment. Filters made of carbon in solid block form, as opposed to granules, are also highly effective in reducing lead. Systems range from inexpensive pour-through carafes to filters that are mounted on faucets, on countertops or under the sink. Cost: $5 to $200.

REVERSE OSMOSIS. These compact units force pressurized water across semipermeable membranes. Lead, arsenic and even some pathogens like Giardia are flushed out of the system--along with 50% to 90% of the water. The purified water that's left behind is passed through yet another filter and stored in a pressurized tank. Under-the-sink models may cost $750.

DISTILLATION. These systems boil water and turn it into vapor, removing most inorganic contaminants like lead and killing any pathogens. The steam is then recondensed into water. However, distillation is not useful for removing volatile chemicals like benzene. Prices start at more than $100.

Unfortunately, none of these systems are worry-free. The instructions for the popular Brita pour-through carafes, for example, tell customers to change the filter every two months or after every 35 gal., whichever comes first. But many people don't count the gallons they use, and if they forget to check the calendar, they can wind up with filtered water that is in worse condition than the stuff that comes from the tap. PUR, based in Minneapolis, Minnesota, has capitalized on this all-too-human habit by marketing a filter that automatically shuts itself off when it has expired.

For most urban and suburban Americans, home treatment systems probably aren't worth the hassle or expense, say independent experts. "In general, the greater risks lie in small community developments like trailer parks that opt not to be part of the water supply of a larger municipality," says Daniel Okun, a retired professor of environmental engineering at the University of North Carolina. "The point is to find out what's going on in your local water supply."

As for disease-causing pathogens, the most cost-effective solution is for the whole community to look after its drinking-water supply. That may require better treatment plants or land purchases to protect watersheds. Without those efforts, the U.S. could end up with a two-tier water system. Those who can afford in-home treatment will have peace of mind, while the rest of the population drinks dirtier and dirtier water.

--Reported by Wendy Cole/Chicago

With reporting by Wendy Cole/Chicago