--- topic: "Well Water Safety" title: "Is Your Well Water Safe?" order: 1 description: "Private wells are not regulated, so testing is up to you. What to test every year, what to add for your region, and how to treat what you find." question: "What should you test for if you drink well water?" answer: "Well water probably needs yearly testing for bacteria, nitrate, pH and dissolved solids, plus local risks such as arsenic and radon." actions: - "Test yearly at a state-certified lab for total coliform bacteria, nitrates, total dissolved solids and pH, and again after flooding, repairs or a change in taste, color or smell [3]." - "Ask your state or county health department which extra tests fit your area (arsenic, radon, uranium, manganese, PFAS) and test for those at least once [3][2]." - "If a result is high, treat that contaminant with a certified system, then retest; for nitrate that means ion exchange, reverse osmosis or distillation, and boiling does not help [6][12]." cautions: - "Infants under six months can develop methemoglobinemia (“blue baby” syndrome) from nitrate in formula water; test before the baby arrives and use water known to be low in nitrate [6][12]." - "Retest in pregnancy or when a child moves in [3]; nitrate is linked to neural tube defects and manganese to lower child IQ, though that evidence is observational [11][7]." - "Boiling concentrates nitrate and does not remove arsenic, uranium or other chemicals, so do not rely on it for chemical contamination [12][6]." confidence: 4 confidenceNote: "Contamination rates and agency testing guidance are consistent across surveys; the health effects of some contaminants (manganese, uranium, PFAS) rest on observational studies." evidenceSummary: rctCount: 0 observationalCount: 7 metaAnalysisCount: 0 totalParticipants: "20,000+ wells; 950+ people" replicated: true newestStudyYear: 2026 references: - id: "1" url: "https://www.epa.gov/privatewells" title: "Private Drinking Water Wells" authors: "US Environmental Protection Agency" year: 2026 journal: "EPA" - id: "2" url: "https://pubs.usgs.gov/sir/2008/5227" title: "Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991-2004" authors: "DeSimone LA" year: 2009 journal: "USGS Scientific Investigations Report 2008-5227" - id: "3" url: "https://www.cdc.gov/drinking-water/safety/guidelines-for-testing-well-water.html" title: "Guidelines for Testing Well Water" authors: "Centers for Disease Control and Prevention" year: 2024 journal: "CDC" - id: "4" pmid: "28605871" title: "Private-well stewardship among a general population based sample of private well-owners" authors: "Malecki KMC, Schultz AA, Severtson DJ, et al." year: 2017 journal: "Sci Total Environ" - id: "5" pmid: "29043784" title: "Estimating the High-Arsenic Domestic-Well Population in the Conterminous United States" authors: "Ayotte JD, Medalie L, Qi SL, et al." year: 2017 journal: "Environ Sci Technol" - id: "6" url: "https://www.cdc.gov/drinking-water/causes/chemicals-that-can-contaminate-tap-water.html" title: "Chemicals That Can Contaminate Tap Water" authors: "Centers for Disease Control and Prevention" year: 2025 journal: "CDC" - id: "7" pmid: "20855239" title: "Intellectual impairment in school-age children exposed to manganese from drinking water" authors: "Bouchard MF, Sauvé S, Barbeau B, et al." year: 2011 journal: "Environ Health Perspect" - id: "8" pmid: "11940450" title: "Renal effects of uranium in drinking water" authors: "Kurttio P, Auvinen A, Salonen L, et al." year: 2002 journal: "Environ Health Perspect" - id: "9" pmid: "40773380" title: "PFAS in Rural U.S. Well Water: Using Participatory Science to Identify and Communicate Results to Address Risks" authors: "Wood E, Mulhern RE, Gibson JM, et al." year: 2025 journal: "Environ Sci Technol" - id: "10" pmid: "30087312" title: "Prevalence of Microbiological and Chemical Contaminants in Private Drinking Water Wells in Maryland, USA" authors: "Murray RT, Rosenberg Goldstein RE, Maring EF, et al." year: 2018 journal: "Int J Environ Res Public Health" - id: "11" pmid: "30041450" title: "Drinking Water Nitrate and Human Health: An Updated Review" authors: "Ward MH, Jones RR, Brender JD, et al." year: 2018 journal: "Int J Environ Res Public Health" - id: "12" url: "https://extension.psu.edu/nitrates-in-drinking-water" title: "Nitrates in Drinking Water" authors: "Robillard PD, Sharpe WE, Swistock BR" year: 2025 journal: "Penn State Extension" --- Nobody tests a private well for you: federal drinking-water rules do not cover wells, and most states do not regulate them either [1]. A national USGS survey found that more than one in five domestic wells had at least one contaminant above a health benchmark [2]. Test every year for bacteria, nitrate, pH and dissolved solids [3], then add the contaminants that are common in your area. ## How it works **Why wells are different.** A public water system is tested, treated and reported on by law. A private well is not: the owner is responsible for making sure the water meets drinking-water standards, and more than 23 million U.S. households rely on private wells [1]. In a Wisconsin survey, about half of well owners had tested in the past ten years, and only 10% of those had tested in the past 12 months [4]. **The yearly four.** The CDC advises testing at least once a year, at a state-certified lab, for total coliform bacteria, nitrates, total dissolved solids and pH. Test again after flooding or land disturbance nearby, after repairs to the well system, when taste, color or smell changes, when someone becomes pregnant, or when a child starts living with you [3]. **What your area adds.** Most contaminants above health benchmarks in wells come from local geology; nitrate and bacteria are the main exceptions, tied to land use. In the USGS survey, radon topped the lower of two proposed limits in about 65% of wells, nitrate, arsenic and manganese were each above benchmarks in roughly 5–7%, and total coliform bacteria turned up in about a third [2]. An estimated 2.1 million people in the contiguous U.S. use well water with predicted arsenic above 10 micrograms per liter (µg/L) [5]. **Nitrate and radon.** Nitrate comes from fertilizer, septic systems and livestock and can lower the blood's ability to carry oxygen, especially in infants [6]. Radon forms in groundwater from natural uranium and radium; breathing in high levels over time can cause lung cancer, and it needs treatment where water enters the house, since point-of-use devices will not reduce it [6]. See [radon](/radon/lung-cancer-risk). **Manganese, uranium, PFAS.** In 362 children, a tenfold higher manganese level in home tap water went with 2.4 fewer IQ points [7]. In 325 people using drilled wells, uranium in water was weakly linked to changes in how kidney tubules handle calcium and phosphate [8]. PFAS (long-lasting industrial chemicals) appeared in 15% of wells in an area with no known sources and in 53–88% of wells at sites with known sources [9]. **Treating what you find.** Match treatment to the contaminant and use certified equipment. If bacteria show up, ask your health department how to disinfect the well and retest [3]. The CDC lists reverse osmosis, ultrafiltration, distillation or ion exchange for arsenic, ion exchange, distillation or reverse osmosis for nitrate, and filters certified under NSF/ANSI 53 or 58 for PFAS; boiling will not remove chemicals [6]. See [choosing a filter](/water-filtration/choosing-a-filter) and, for city water, [testing your water](/water-filtration/testing-your-water). ## The evidence in detail **National survey.** The USGS sampled as many as 2,167 domestic wells in 30 aquifers between 1991 and 2004; most contaminants were measured in 1,389 wells. About 23% of wells had at least one contaminant above an enforceable limit or a health-based screening level, though no single contaminant exceeded its benchmark in more than 8% of wells. Radon was above the lower proposed limit (300 pCi/L) in about 65% of wells but above the higher one (4,000 pCi/L) in about 4%. Nitrate, arsenic, manganese, strontium and gross alpha radioactivity were each above benchmarks in roughly 5–7%, uranium in about 1–2%, and manufactured organic compounds in 0.8%. Total coliform bacteria were detected in about 34% of wells and E. coli in about 8% [2]. The data are two decades old and describe a sample of aquifers, not your well. **A local study.** Murray and colleagues sampled 118 wells in four Maryland counties: 43.2% failed at least one federal health-based standard. Total coliform, fecal coliform, enterococci and E. coli were found in 25.4%, 15.3%, 5.1% and 3.4% of wells, and about 3.4% exceeded the nitrate standard. Nearby animal feeding operations showed no statistically significant link to bacteria, a reminder that the cause of contamination is often not obvious [10]. **Arsenic.** Ayotte and colleagues built a model from arsenic measurements in 20,450 domestic wells. About 44.1 million Americans use domestic wells, and 2.1 million (95% CI 1.5–2.9 million) in the contiguous states are predicted to be using water above 10 µg/L. This is a prediction for areas, not a measurement at each home, and some regions had sparse data [5]. **Nitrate.** A review of epidemiologic studies since 2005 (more than 30 studies) found that, besides infant methemoglobinemia, the strongest evidence links drinking-water nitrate to colorectal cancer, thyroid disease and neural tube defects. Many studies saw higher risk at levels below the legal limit, but exposure assessment was often weak [11]. **Manganese.** Bouchard and colleagues studied 362 children aged 6–13 in groundwater-supplied communities. Median tap manganese was 34 µg/L (range 1–2,700). Each tenfold increase was associated with a 2.4-point lower IQ (95% CI −3.9 to −0.9) after adjusting for maternal intelligence, family income and other factors, and children in the highest quintile scored 6.2 points lower than those in the lowest. Hair manganese tracked water intake, not diet. The study was cross-sectional, so it cannot prove cause [7]. **Uranium.** Kurttio and colleagues measured uranium in water and urine in 325 people on drilled wells (median 28 µg/L, maximum 1,920). Higher urinary uranium was associated with greater fractional excretion of calcium and phosphate, signs of altered kidney tubule function, but not with creatinine clearance or urinary albumin. The authors said the clinical relevance was not easy to establish [8]. **PFAS.** Wood and colleagues had 271 well users in four states collect tap water for analysis of 25 PFAS. PFAS were found in 15% of wells in an area with no known sources, some above a health guideline, and in 53–88% of wells at sites with known sources. Concentrations were higher closer to production facilities, Superfund sites, spill sites and federal facilities. When filters were recommended, 49% of households installed one [9]. **Null and conflicting results.** Findings for the lesser-known contaminants are modest or uncertain: uranium showed no effect on glomerular function [8], the manganese link is cross-sectional [7], and nitrate associations below the legal limit may reflect confounding [11]. None of these changes the baseline advice to test for bacteria and nitrate every year. **Bottom line (confidence 4 of 5).** Private wells have no regulator, and a meaningful share fail at least one health benchmark. Yearly testing for bacteria, nitrate, pH and dissolved solids is the sound baseline, with arsenic, radon, uranium, manganese and PFAS added where your geology or neighbors suggest them. Evidence on lower-dose effects of manganese, uranium and PFAS is still observational.