The Flint, Mich., water crisis left many Americans questioning the safety of their drinking water. Only about half of Americans feel “very confident” in the safety of their tap water, with another third “moderately confident,” according to an Associated Press-GfK poll taken during the crisis. Moreover, a 2017 Gallup poll reported that two-thirds of Americans worry “a great deal” about pollution in their drinking water.

These concerns may not be unfounded, as the U.S. Environmental Protection Agency (EPA) found one or more violations of EPA water-related rules affecting nearly 27 million people in fiscal year 2016 (not necessarily indicating unsafe water). This finding covers the 95 percent of the U.S. population served by community water systems, not private water sources. A recent Harvard study on polyfluoroalkyl and perfluoroalkyl substances (PFASs), industrial chemicals known to cause cancer and immunodeficiency, found PFASs in 6 million Americans’ tap water. The Harvard study warned that this number could be considerably higher since there were no data on PFASs levels for water affecting nearly one-third of U.S. citizens.

In response to these types of findings, many consumers are purchasing water filters or whole-house filtration systems. Here’s what you need to know to make a smart buying decision.

EPA rules

The EPA sets legal limits for drinking water on more than 90 known harmful contaminants and also establishes water-testing schedules and rules around methods for handling and purifying water that public utilities must follow.

As part of these rules, the EPA requires that community water systems serving more than 10,000 people publish the results of water tests for the public. These publications are called Consumer Confidence Reports (CCR).

Before you choose a water filtration system, you’ll want to access your local water utility’s CCR, says Amanda Fisher, business development manager for UL’s water systems program, in an Inside UL article. The CCR outlines contaminants detected in the water supply and whether any of those levels exceed the EPA’s drinking water standards – key information to know when choosing your water filter type. Another good resource is the Environmental Working Group’s Tap Water Database.

Home Water Tests

Because of the Flint water crisis – which local activists, brought to the world’s attention – some consumers choose to have their home water tested. Another reason to consider home water testing is if your plumbing system is older. Consumer Reports advises consumers to get a home test for lead if your home plumbing system is pre-1986 when lead-free pipes became required by law. Additionally, the EPA suggests getting your water tested before installing a whole-house water filtering system. A certified lab in your state can help advise on what tests to perform, as well as conduct the testing.

If you have a private water system, it is your responsbility to test it. You’ll want to test it annually for total coliform bacteria and E. coli bacteria, advises PennState Extension, and test for pH and total dissolved solids every three years. Also, include specific tests based on the adjacent land uses every three years, and test as needed if drinking water issues, like stains and odd tastes, occur.

Choosing the Right Water Filter

Once you examine your CCR or have your water tested, you’ll have a better idea of what contaminants you’ll want a water filter to remove. Then, choose a type of filter system that claims to remove these contaminants.

When evaluating different water filters, you might see testing and certification standards listed, such as NSF/ANSI 42 and NSF/ANSI 53. NSF/ANSI 42 applies to filters making aesthetic-reduction claims about chlorine, particulate matter, etc. NSF/ANSI 53 evaluates products making health-related reduction claims about known toxins, like lead, arsenic, nitrites, volatile organic compounds (VOC), microbial cysts, etc.

Both standards outline criteria for literature that must accompany each system, including specific requirements for the data label, the manual and the performance data sheet. “The language needs to be specific and include actual data as well as clearly state the percentage of contaminant reduced by the product,” says UL Project Engineer Irina Garbar. This literature is important for determining what the filter does and does not do.

One additional must: Choose a filter that has been tested and certified to the appropriate NSF standards by NSF International or a third party like UL. This means that the design has undergone a rigorous testing process to help ensure that it removes the toxins it claims to remove, and without leaching other chemicals from the product into the drinking water.

Putting all of these steps together, including knowing what contaminants you want to filter before choosing a water filter, will help you get the best value for your money.