Water filters: reading NSF/ANSI labels and comparing cost per gallon

Types of filters

• Pitchers: filter water as you pour it, and fit in a refrigerator. Cartridges are replaced on a schedule.
• Faucet-mount filters: attach to a tap. Check that the fit matches your faucet.
• Refrigerator filters: built into the fridge and made for specific models.
• Under-sink and countertop systems: connect to the water line or sit on the counter. They usually need installation or setup.
• Whole-house systems: treat water where it enters a home. Often installed by a professional.

What NSF/ANSI certification means

NSF/ANSI standards are published standards used by independent certifiers to test filters for specific claims. Different standards cover different things, for example taste and odor, or specific substances, and a product is certified only for the claims that are listed. A label that says certified does not mean the filter has been tested for everything. The performance data sheet that comes with the product, or that is on the certifier's website, shows exactly what a filter is certified for. We do not say what any filter removes, and we do not make health claims. Read the data sheet to see what a specific product is tested and certified for.

Understanding your water

• Your water utility publishes an annual water quality report for customers. It lists what the utility tests for.
• If you use a private well, ask your local health department about testing.
• If you have a concern about your water, a certified laboratory can test a sample. Choose a filter based on the results, not only on marketing.
• Flow rate and capacity: check them for the system you choose.

Our angle: cost per gallon, then replacement timing

A cheap filter housing with expensive cartridges can cost more than a pricier system with cheap cartridges. The label states a rated capacity for each cartridge, in gallons. Divide the cartridge price by that capacity to get the price per gallon. Then check the replacement schedule, since a filter that is used past its rated capacity may no longer do what it was certified for. Add the housing cost spread over the years you expect to use it. Compare systems on cost per gallon rather than price per cartridge.

1. Find the rated capacity of a cartridge in gallons.
2. Divide the cartridge price by that capacity.
3. Add the housing price spread over the years of use, and compare.

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