Water, and plenty of it, is crucial to health — unless it’s not clean, in which case it can make you or your loved ones sick. If you suspect that the water flowing from your kitchen tap is less than pure, a water filter can help. The trick is choosing the right one. There’s a boatload of choices, so use these tips to find the best water filter for your faucet and the icky things that come out of it.

Know what’s in the water. The specific contaminants in your water can have a bearing on the filter you use. Before you start shopping, learn all you can about the quality of your water. “Your water company sends out a consumer confidence report each year," says Paul Pestano, a research analyst at the nonprofit Environmental Working Group. You also can look up the annual report on your water company's website. It will spell out where your tap water originates, list any contaminants lurking in it and indicate if any are at worrisome levels.

Learn the source of your water’s problems. Even tap water that’s been treated can contain contaminants, Pestano says. These include carcinogens (cancer causing substances) as well as chemicals that can harm the nervous system, endocrine system and the unborn babies of women who ingest the water during pregnancy. Contaminants can make their way into tap water from a variety of sources, including farm runoff that contains manure and fertilizer, runoff from sewage plants and factory waste.

Find your filter. There are two types of water filter:

  • Carbon filters. They rely on charged, highly absorbent carbon to trap impurities. The label on a carbon water filter will list the contaminants it can remove. Typically, says Pestano, carbon filters remove some of the more common ones such as chlorine and lead as well as volatile organic compounds (VOCs). Some claim to improve how water tastes and smells as well. Many carbon water filters attach right to the faucet and sell for under $40.

  • Reverse osmosis filtering systems. These push water through a semipermeable membrane that can trap any particles that are larger than water molecules. This process can’t remove all contaminants — for example, chlorine and VOCs.For that reason, many reverse osmosis systems incorporate a carbon filter.

    Reverse osmosis filtering systems must be installed and cost from $200 to $400 or more. They also use a lot of water — from three to 20 times the amount being filtered.

    Whichever type of water filter you buy, make sure that it’s certified by either the California Department of Public Health or NSF International, an independent organization that tests and certifies products ranging from dietary supplements to medical devices.

Shopping by contaminant

If you need to filter out a specific problematic pollutant, NSF International’s Contaminant Reduction Claims Guide can help you figure out the right filter type for the job and the filtering capacity, in parts per billion (ppb), needed. It allows you to search for this information based on the bug you’re trying flush out.

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.