Filtered water is good for you. It removes contaminants that municipal treatment doesn’t fully eliminate, including chlorine byproducts, lead, pesticides, and industrial chemicals. For most people, a basic carbon filter meaningfully improves both the taste and safety of tap water. That said, the type of filter matters, maintenance matters, and in some cases filtration can remove beneficial minerals you’d rather keep.
What’s Actually in Your Tap Water
Municipal water in the U.S. is treated and regulated, but “safe by legal standards” and “free of concerning substances” aren’t the same thing. The EPA sets limits for dozens of contaminants, yet many of those limits haven’t been updated in years, and some chemicals are present at levels below the legal maximum but above what newer research suggests is ideal.
The contaminants most relevant to your health fall into a few categories. Lead is a major one: the EPA estimates there are still 4 million lead service lines delivering water to homes across the country. Even low levels of lead exposure accumulate over time and affect the brain, kidneys, and cardiovascular system. Chlorine and its byproducts are added intentionally to kill bacteria, but they create compounds linked to increased cancer risk with long-term exposure. Then there are PFAS, a class of industrial chemicals sometimes called “forever chemicals” because they don’t break down in the environment or your body. The EPA has issued health advisories for several PFAS compounds and set enforceable limits for the most studied ones.
Microplastics are a newer concern. A systematic review and meta-analysis found that tap water contains an average of about 57 microplastic particles per liter. The long-term health effects are still being studied, but early evidence points to inflammation and potential hormone disruption. Beyond these, tap water can contain trace amounts of pesticides, pharmaceutical residues, and volatile organic compounds depending on your local water source and infrastructure.
What Different Filters Actually Remove
Not all water filters do the same job. The differences are significant enough that choosing the wrong type can leave you with a false sense of security.
Activated carbon filters (the kind in most pitcher filters and faucet attachments) are effective at removing chlorine, improving taste and odor, and pulling out volatile organic compounds. The EPA notes that granular activated carbon achieves removal rates up to 99.9% for many VOCs. Carbon filters also reduce some pesticides and industrial solvents. They’re affordable, easy to use, and handle the most common complaints about tap water. However, standard carbon filters don’t reliably remove lead, fluoride, PFAS, or dissolved minerals and salts.
Reverse osmosis systems push water through a membrane fine enough to strip out dissolved solids, heavy metals, PFAS, radionuclides, and most synthetic organic chemicals. They produce the most thoroughly purified water available at home. The tradeoff is cost, complexity (most require under-sink installation), water waste (they typically send two to four gallons down the drain for every gallon filtered), and the removal of beneficial minerals along with the harmful stuff.
Specialty filters exist for specific concerns. Some carbon block filters are engineered to handle lead and cysts like Cryptosporidium. UV filters kill bacteria and viruses without removing chemicals. Ceramic filters block microorganisms but leave dissolved contaminants alone.
How to Know a Filter Does What It Claims
The most reliable way to evaluate a water filter is through its NSF/ANSI certification. These are independent testing standards, and each one covers different contaminants:
- NSF/ANSI 42 covers aesthetic improvements: chlorine, taste, odor, and particulates.
- NSF/ANSI 53 covers health-related contaminants. It includes over 50 claims, with the most common being lead, Cryptosporidium, VOCs, and chromium.
- NSF/ANSI 401 covers emerging contaminants like prescription drug residues, over-the-counter medications, herbicides, and pesticides.
If a filter carries one of these certifications, it’s been independently tested to reduce those specific contaminants. A pitcher filter certified to NSF 42 but not 53 will make your water taste better without necessarily making it safer. Check the packaging or the manufacturer’s website for the specific certification numbers.
The Mineral Removal Question
One legitimate concern about filtration, especially reverse osmosis, is that it strips out calcium and magnesium along with contaminants. These minerals contribute to your daily intake in ways that matter more than you might expect. Research on populations in industrialized countries has consistently found that most people already fall short of recommended calcium and magnesium levels through diet alone. One French study found that 62% of women consumed less than the recommended 1,200 mg of daily calcium, and 77% fell short on magnesium.
Tap water isn’t your primary source of these minerals, but depending on your local water hardness, it can contribute meaningfully. Water with moderate mineral content provides roughly 50 to 70 mg of calcium per liter and smaller amounts of magnesium. If you use a reverse osmosis system, you can compensate by eating mineral-rich foods or adding a remineralization filter stage, which many RO systems now include. Basic carbon filters don’t remove minerals, so this concern doesn’t apply to pitcher filters or faucet-mounted units.
Dirty Filters Can Make Things Worse
A filter you forget about can become a liability. Carbon filters that sit past their replacement date lose their ability to trap contaminants, and the warm, moist environment inside a filter housing is ideal for bacterial growth. Biofilms, thin layers of bacteria that cling to surfaces, form inside filter cartridges and the plumbing connected to them. Once established, biofilms are difficult to eliminate completely. They colonize the interior of the faucet itself, feeding on nutrients in the filtered water.
Refrigerator water dispensers are a particular concern. The water collects in a reservoir, and heat from the refrigerator’s motor warms it before the cooling system kicks in, creating conditions that encourage bacterial multiplication. In at least one documented case, the bacterial strain found in a patient’s infection matched the DNA fingerprint of organisms growing in their refrigerator’s water dispenser.
The fix is straightforward: replace filter cartridges on schedule. Most pitcher filters need replacement every two to three months or 40 gallons, whichever comes first. Faucet-mounted filters last around three months. RO membranes typically last one to three years depending on water quality and usage. If your area issues a boil-water advisory, replace all filters once the advisory is lifted.
Who Benefits Most From Filtering
Filtered water offers the biggest health advantage for people in specific situations. If your home was built before 1986, there’s a meaningful chance your plumbing contains lead solder or you’re connected to a lead service line. A filter certified to NSF 53 for lead reduction is a practical safeguard, especially for households with young children or pregnant women, since lead is most damaging during development.
People with compromised immune systems benefit from filters that remove cysts like Cryptosporidium and Giardia, which can cause severe illness in people whose bodies can’t fight them off easily. Those living near agricultural or industrial areas may face higher levels of pesticides, solvents, or PFAS in their water supply.
For everyone else, a carbon filter is a reasonable, low-cost upgrade. It won’t transform dangerous water into safe water on its own, but it removes the most common irritants and reduces your cumulative exposure to chlorine byproducts and organic chemicals over years of daily drinking. If you want to know exactly what’s in your water before choosing a filter, your local utility is required to publish an annual Consumer Confidence Report listing detected contaminants and their levels. That report is the best starting point for deciding how much filtration you actually need.