Choosing a Water Filter for What Is in Your Water

Water filters are sold with promises of purer, healthier water, and the range of options can be confusing: pitchers, faucet attachments, under-sink systems, reverse osmosis units and whole-house filters. The right choice depends entirely on what is in your water. A filter that removes chlorine taste does nothing for bacteria, and one that removes lead may not touch nitrates. Working through three questions in order avoids buying the wrong filter, or one you don't need at all.

Question 1: What is in your water?

If you are on public water in the US, your utility must publish an annual water quality report, called a Consumer Confidence Report, usually by July 1 each year. It lists the contaminants detected and whether they meet federal standards. Many are available on the utility's website or through the EPA. Most public water in the US meets federal standards, but taste, odor and specific local issues can still lead people to filter.

If you have a private well, you are responsible for testing it. The CDC recommends testing well water at least once a year for total coliform bacteria, nitrates, total dissolved solids and pH, and more often if anything changes, such as after flooding. Depending on local geology, testing for arsenic, radon, uranium or other contaminants may also be advised. Local health departments can recommend certified laboratories.

Consider your plumbing. Even if your water supply is clean, lead can enter drinking water from lead service lines, older pipes, solder or fixtures, especially in homes built before 1986 in the US. Many utilities offer lead testing, and some are replacing lead service lines under federal rules.

Question 2: Which filter matches the problem?

Taste and odor, such as chlorine. Activated carbon filters, used in most pitchers, refrigerator filters and faucet-mounted filters, reduce chlorine taste and odor and some organic chemicals.

Lead. Many carbon-based pitchers, faucet filters and under-sink systems are certified to reduce lead, but not all. Look for certification to NSF/ANSI Standard 53 for lead reduction. Boiling water does not remove lead and can concentrate it.

PFAS. Per- and polyfluoroalkyl substances, sometimes called "forever chemicals," have been found in many water supplies. In 2024, the EPA set the first national drinking water limits for several PFAS, with compliance deadlines for utilities in the following years that have since been under review. Certain activated carbon and reverse osmosis systems are certified to reduce PFOA and PFOS under NSF/ANSI 53 or 58, or the newer NSF/ANSI P473 standard.

Nitrates, arsenic, fluoride and dissolved solids. Reverse osmosis systems, usually installed under the sink, push water through a fine membrane and remove a wide range of dissolved contaminants. They also remove beneficial minerals, waste some water in the process, and require maintenance. Look for certification to NSF/ANSI 58.

Bacteria and viruses. Most household filters are not designed to make microbiologically unsafe water safe. Ultraviolet treatment systems, often used for wells, can inactivate many microbes in clear water. During a boil-water advisory, follow the advice from authorities rather than relying on a typical filter.

Hard water. Hardness from calcium and magnesium is not a health concern, but it leaves scale on kettles and fixtures. Water softeners address hardness through ion exchange; they are not filters for contaminants and add sodium or potassium to the water.

Sediment. Whole-house sediment filters protect appliances and plumbing from sand and rust, particularly with well water.

Question 3: How will you use and maintain it?

Pitchers are inexpensive and easy but filter slowly and hold limited water.
Faucet-mounted filters filter on demand but don't fit all faucets and can slow the flow.
Under-sink systems filter more water with less fuss, but require installation.
Whole-house systems treat all water entering the home and are mainly for sediment, chlorine or specific well water problems.

Whatever you choose, replace cartridges on schedule. An overused filter loses effectiveness and can even harbor bacteria. Many products have indicators or app reminders.

Checking certifications

Marketing claims such as "removes 99 percent of contaminants" are meaningless without specifics. Independent certification organizations, including NSF International, the Water Quality Association and IAPMO, test filters against published standards and list which contaminants each product is certified to reduce. Check the specific contaminant on the certifier's online database, not just a general certification mark on the box.

Questions to ask before buying

Which specific contaminants am I trying to reduce, and is this product certified for them?
How often do filters need replacing, and how much do replacements cost over a year?
How much filtered water does my household use each day?
Do I rent, and will I be allowed to install an under-sink or whole-house system?

Bottled water is not automatically better

Bottled water is regulated differently from tap water and is not necessarily purer. It costs far more and produces plastic waste. For most households with safe tap water, a certified filter that addresses specific concerns, or no filter at all, is a better choice.