Water is the most fundamental input to human health—we drink it, cook with it, and absorb it through our skin. Yet most people have little idea what is actually in their home’s water supply, or what happens to it between the source and the tap. This guide covers what you need to know about home water quality: the contaminants of concern, how to test, and how to filter.
What’s in Your Tap Water
Municipal water in the US and most developed countries is treated to meet legal safety standards—meaning it is free of immediately dangerous pathogens and most acute toxins. But “legally safe” and “optimally healthy” are not synonymous. Several categories of contaminants pass through conventional treatment or are added by it.
Disinfection byproducts (DBPs): Chlorine and chloramine, added to kill pathogens, react with naturally occurring organic matter to form halogenated byproducts including trihalomethanes (THMs) and haloacetic acids (HAAs). These compounds are associated with increased cancer risk and reproductive harm at levels regularly found in treated municipal water.
Lead: Lead pipes and lead solder remain in the plumbing of millions of US homes, particularly those built before 1986. Lead leaches into water, particularly when water is corrosive or stands in pipes. There is no safe level of lead exposure, particularly for children. The Flint, Michigan crisis brought this issue to national attention, but lead in household plumbing is a widespread and ongoing problem.
Fluoride: Added to most US municipal water supplies for dental health benefits, fluoride is also a topic of ongoing controversy. At levels above 4 mg/L it is classified as a contaminant. At current US levels (0.7 mg/L), most regulatory bodies consider it safe, though some research associates long-term exposure with thyroid effects and, in children in high-fluoride areas, with IQ impacts.
PFAS (per- and polyfluoroalkyl substances): This class of industrial chemicals—used in non-stick cookware, food packaging, firefighting foam, and many industrial applications—is persistent in the environment and increasingly detectable in water supplies near industrial or military sites. PFAS are associated with cancer, thyroid disruption, immune suppression, and developmental harm. The EPA has established a maximum contaminant level (MCL) of 4 parts per trillion for PFOA and PFOS (among the best-studied PFAS) as of 2024.
Nitrates: High nitrate levels, often from agricultural runoff, are associated with methemoglobinemia (“blue baby syndrome”) in infants and emerging research links chronic adult exposure to colorectal cancer and thyroid effects.
Pharmaceuticals and emerging contaminants: Trace levels of pharmaceuticals, hormones, and other emerging contaminants are detectable in many water supplies. Long-term health effects are uncertain but are an area of active research.
Well Water: Different Risks
Private wells are not regulated by federal standards and require individual testing and maintenance. Well water risks vary significantly by region and local geology but include: arsenic (natural; common in New England and the West); radon (natural); nitrates (agricultural areas); bacteria and pathogens (surface contamination); and industrial and agricultural chemicals (local contamination).
All well owners should test annually at minimum for bacteria, nitrates, and pH, and periodically for heavy metals, arsenic, and other contaminants specific to their region.
How to Test Your Home Water
Start with your annual Consumer Confidence Report (CCR), which municipal water utilities are required to send to customers. This reports on regulated contaminants tested at the distribution system level—note that it does not reflect what happens in your home’s plumbing.
For home-specific testing, certified mail-in labs (NSF, EPA-certified) provide comprehensive panels. Tap Score and National Testing Laboratories are well-regarded options. A basic panel covers lead, chlorine, bacteria, and common metals; advanced panels include PFAS, DBPs, nitrates, and emerging contaminants.
Filtration Options
No single filter removes all contaminants. Understanding what’s in your water—through testing—guides filter selection.
Activated carbon (pitcher, under-sink, or whole-house): Removes chlorine, chloramines, VOCs, many pesticides, and improves taste and odor. Does not remove lead, heavy metals, nitrates, PFAS, or fluoride without specifically rated media.
Reverse osmosis (RO): Removes a broad spectrum of contaminants including lead, nitrates, arsenic, most PFAS, fluoride, and dissolved solids. The gold standard for drinking water purification. Drawbacks: slow flow rate, wastes water (3–4 gallons per gallon produced in standard units), and removes beneficial minerals. A remineralization filter stage can address the latter.
NSF-certified filters: Look for filters certified to NSF/ANSI Standard 53 (health effects contaminants) and Standard 58 (RO systems). NSF certification means the filter has been independently tested to remove what it claims.
Whole-house filtration: Sediment and carbon filters at the point of entry address water used for bathing and laundry as well as drinking—relevant because skin absorption and inhalation of shower steam can be significant exposure routes for chlorine and volatile chemicals.
The Lead Problem
If your home was built before 1986, or if you live in a multi-unit building with shared plumbing, lead in drinking water is a real possibility. The only way to know is to test. The fix is filtration: a certified NSF 53 filter for lead removal at the kitchen tap (and ideally the bathroom where children’s water comes from) is effective and relatively affordable. This is particularly important for homes with young children or pregnant women.
Understanding and addressing your home’s water quality is among the most direct and evidence-backed wellness interventions available. The investment in testing and filtration—typically a few hundred dollars—buys years of reduced exposure to contaminants that have measurable effects on health over time.