Photo: Water flowing from a tap

Finding out what's in your water will help determine what kind of filter you will need.

Photograph by Péter Gudella/Shutterstock

Updated by Eliza Barclay

for National Geographic

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Though U.S. drinking water has been protected under the Safe Drinking Water Act since 1974, experts warn that tap water increasingly does not meet health-safety guidelines.

A recent investigation by The New York Times found that, since 2004, some 62 million people in the U.S. have been exposed to drinking water contaminated with thousands of chemicals—albeit in low concentrations—that are not regulated under federal law.

Of course, the best way to ensure clean and safe drinking water is to protect the source. Watersheds act as natural filters that remove chemicals, pollutants, and sediment. Citizens can also urge Congress and the federal government to update the Safe Drinking Water Act to include and regulate potentially hazardous new chemicals.

In the meantime, many consumers are turning to home water filters for added peace of mind.

The first step in determining whether a water filter might make your tap water cleaner is to find out what’s in your water, and if it contains any dangerous, unregulated chemicals.

If possible, check out your annual water-quality report—also called a consumer-confidence report—from your water supplier. Some reports are available on the U.S. Environmental Protection Agency (EPA)’s Web site. These reports can be difficult to interpret, so download a guide to reading them at the Campaign for Safe and Affordable Drinking Water’s Web site.

The Environmental Working Group’s “What’s in your water?” tool is another useful mine of information on local water supplies. The nonprofit recommends that most people in the U.S. filter their tap water.

If you decide to purchase a water filter, experts recommend selecting filters certified by the National Sanitation Foundation, which tests products to ensure that they remove what is required by water-filter manufacturers.

The foundation maintains an extensive database searchable by type of water treatment product.

No filter will remove every contaminant, in part because the list of risky chemicals keeps growing.  But here are the most common types of filters and the major contaminants they are designed to trap:

  1. Carbon filters include countertop pitchers, faucet-mounted models, undersink models (which 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.
  2. Reverse-osmosis systems push water through a semipermeable membrane, which acts as an extremely fine filter. They're often used in conjunction with carbon filters. However, these systems waste 4 to 9 gallons (15 to 34 liters) of water for every gallon (3.8 liters) filtered.  What they remove: Chemicals carbon filters may miss, including perchlorate, sulfates, fluoride, industrial chemicals, heavy metals (including lead), chlorine byproducts, chlorides (which make water taste salty), and pharmaceuticals.
  3. Ultraviolet light units disinfect water, killing bacteria. Countertop units can be found for under U.S. $100, but most whole-house units cost $700 and upward. What they remove: Bacteria. Experts recommend using them with carbon filters to remove other contaminants.
  4. 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 contaminants, or, in a pinch, buy distilled water.  What they remove: Heavy metals (including lead), particles, total dissolved solids, microbes, fluoride, lead, and mercury.

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