Do You Really Need a Water Filter?

ll sorts of nasties—lead, mercury, radium, nitrates, norovirus, agricultural runoff, , and more—can lurk in your water. No surprise, then, that about 40% of U.S.

homes But the options are endless, from simple $20 charcoal-filter pitchers to reverse osmosis, point-of-entry, or ultraviolet filters. Depending on what you choose, a water filter can cost you tens of dollars, or thousands. Here’s what to know if you’re considering a water filter—and how to tell if you need one.

Plenty of public systems produce impressively pristine water. New York City, for example, puts out a billion clean gallons of water a day, says environmental health scientist David Nadler of the New York Institute of Technology. But the water that leaves the reservoir and treatment plant is not necessarily the same water that comes out of your tap.

In cities, water is typically pumped up to rooftop tanks, which feed the flow down to spigots via gravity. If the tank is not kept clean, the water will suffer too. Older buildings may still have lead pipes or asbestos in the walls, which can contaminate water as well.

“Your supply company could send you the purest water in the world. But if your pipes are old and have lead in them, there's really no protecting you,” says Nadler. “You’re at the mercy of your plumbing.

” : In cities, suburbs, and rural areas, periodic flooding can contaminate otherwise-clean water with industrial or agricultural runoff or sewer overflow. Algae and fungi, which bl.