--- topic: "Water Filtration" title: "What's in Your Water" order: 1 description: "Common contaminants found in US tap water and why they matter for your health" question: "Is tap water that meets legal limits still a health risk?" answer: "Tap water meeting legal limits likely still carries some risk, mainly from lead and PFAS; effects of microplastics and drug traces are unclear." actions: - "Check the EWG Tap Water Database for your area; it compares utility test data with legal limits and stricter health guidelines [3]." - "If your home was built before 1986, run cold water for 30 seconds to 2 minutes before use and use a certified filter [5]." - "Compare your utility's PFAS results with the 2024 EPA limit of 4 parts per trillion for PFOA and PFOS." cautions: - "No level of lead is safe, and children's developing brains are most at risk; the EPA action level is 15 ppb [5]." - "Chlorine is essential against waterborne disease; the concern is its byproducts (trihalomethanes and haloacetic acids), which the EPA regulates [1]." - "Health effects of microplastics and trace pharmaceuticals are still emerging, far less certain than for lead and PFAS." confidence: 3 confidenceNote: "Lead evidence comes from CDC guidance and PFAS limits from EPA regulation; the article cites no human studies, and microplastic and pharmaceutical effects are not yet established." evidenceSummary: rctCount: 0 observationalCount: 0 metaAnalysisCount: 0 replicated: false newestStudyYear: 2024 references: - id: "1" url: "https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations" title: "National Primary Drinking Water Regulations" authors: "US Environmental Protection Agency" year: 2024 journal: "EPA" - id: "2" title: "Tap Water Exposures, Toxicities, and Health Effects: A Review and Risk Assessment" authors: "Levin R, Villanueva CM, Beane Freeman L" year: 2021 journal: "Environmental Science & Technology" - id: "3" url: "https://www.ewg.org/tapwater/" title: "EWG Tap Water Database" authors: "Environmental Working Group" year: 2024 journal: "EWG" - id: "4" title: "PFAS in drinking water and human health effects: A review" authors: "Cordner A, De La Rosa VY, Schaider LA, Rudel RA, Richter L, Brown P" year: 2021 journal: "Environment International" - id: "5" url: "https://www.cdc.gov/drinking-water/about/lead-in-drinking-water.html" title: "Lead in Drinking Water" authors: "Centers for Disease Control and Prevention" year: 2024 journal: "CDC" --- US tap water is treated to meet federal safety standards, but "legal" doesn't always mean "harmless." Dozens of contaminants show up at levels that are technically allowed yet linked to health concerns in newer research. The most common ones to know about are chlorine disinfection byproducts, lead from old pipes, PFAS "forever chemicals," microplastics, and trace pharmaceuticals [3]. Understanding what's actually in your water is the first step toward deciding whether you need a filter — and which kind. ## Chlorine and Disinfection Byproducts Utilities add chlorine or chloramine to kill bacteria, which is essential for preventing waterborne disease. But when chlorine reacts with organic matter in the water, it creates disinfection byproducts (DBPs) like trihalomethanes (THMs) and haloacetic acids (HAAs) [1]. The EPA regulates THMs at 80 parts per billion. ## Lead There is no safe level of lead exposure [5]. Lead enters tap water not from the source but from the infrastructure — lead service lines, solder joints, and brass fixtures in homes built before 1986. The EPA's action level is 15 ppb, but the CDC and American Academy of Pediatrics emphasize that any detectable lead poses a risk to children's neurological development [5]. The 2014 Flint, Michigan crisis made national news, but EWG testing shows detectable lead in water systems serving millions of Americans [3]. ## PFAS (Per- and Polyfluoroalkyl Substances) PFAS are synthetic chemicals used in nonstick coatings, food packaging, and firefighting foam since the 1950s. They earned the name "forever chemicals" because they don't break down in the environment or the human body. In 2024, the EPA finalized the first national drinking water standard for six PFAS compounds at 4 parts per trillion for PFOA and PFOS. Prior to this, there was no enforceable federal limit. ## Microplastics Microplastics (particles under 5mm) have been detected in tap water worldwide, including US municipal systems. A 2018 study found microplastic fibers in 94% of US tap water samples tested. Research on health effects is still emerging, but concerns center on the particles themselves and the chemical additives they carry (phthalates, bisphenols, flame retardants). ## Pharmaceuticals and Hormones Trace amounts of prescription drugs — antibiotics, antidepressants, synthetic estrogens — enter the water supply through human excretion and improper disposal. Conventional water treatment does not fully remove them. Detected concentrations are typically in the low nanogram-per-liter range, well below therapeutic doses, but the effects of chronic low-level exposure and chemical mixtures are not yet well understood. ## How Standards Are Set — and Where They Fall Short The EPA's National Primary Drinking Water Regulations set Maximum Contaminant Levels (MCLs) for about 90 contaminants [1]. These MCLs are legally enforceable, but they represent a balance between health goals, treatment feasibility, and cost — not purely health-based thresholds. The EPA also publishes Maximum Contaminant Level Goals (MCLGs), which are non-enforceable health targets. For lead and several carcinogens, the MCLG is zero, meaning any exposure carries some theoretical risk [1]. The EWG Tap Water Database compiles utility testing data and compares results against both legal limits and their own health guidelines, which are often 10–100x stricter than MCLs [3]. For example, the legal limit for chromium-6 (hexavalent chromium) is 100 ppb based on a 1991 standard, while California's public health goal — based on more recent cancer data — is 0.02 ppb. The CDC emphasizes that lead risk is heavily infrastructure-dependent. Homes with lead service lines, which the EPA estimates at 6–10 million nationwide, face the highest exposure. Running cold water for 30 seconds to 2 minutes before use and using certified filters are the primary recommended mitigations [5].