In 1974, Congress passed the Safe Drinking Water Act to protect Americans from contaminated tap water. The law covers every public water system in the country — from New York City's reservoirs to the smallest community system serving 25 people.
It does not cover a single private well.
That's not a loophole. It's by design. The SDWA explicitly exempts private domestic wells from federal regulation. No testing requirements. No treatment standards. No reporting obligations. No enforcement mechanism.
How many wells are we talking about? The EPA estimates more than 23 million households rely on private wells — roughly 13 to 15 million individual wells across the country. That’s more wells than there are Starbucks, McDonald’s, and Walmart locations combined.
The result: approximately 43 million Americans — about 15 percent of the U.S. population — drink water from wells that no government agency is required to monitor, test, or regulate.
The Scale of the Problem
The U.S. Geological Survey's study of 2,100 private domestic wells across the country produced a finding that should concern anyone with a well on their property: water pumped from about one in five wells contained one or more contaminants at a concentration greater than a human-health benchmark for drinking water.
That's not one in five wells with detectable traces of something. That's one in five exceeding levels the EPA considers safe.
The CDC frames it more starkly: from 1971 through 2008, the proportion of waterborne disease outbreaks associated with private water sources increased — even as outbreaks from public systems declined. The regulatory framework that protects 85 percent of Americans is working. The 15 percent on private wells are increasingly on their own.
What's in the Water
The USGS study found contaminants that fall into several categories, and the most common aren't the ones most people expect:
Inorganic chemicals dominate the problem. Metals, radionuclides, and nitrate were the contaminants most frequently found at concentrations above health benchmarks. Most of these — except nitrate — come from natural geological sources, not industrial pollution. The rock your well is drilled through can be the source.
Arsenic is perhaps the most alarming. A USGS study focused on arsenic estimated that approximately 2.1 million people are using wells with arsenic levels above the EPA's maximum contaminant level of 10 parts per billion. Chronic arsenic exposure is linked to bladder, lung, and skin cancers, cardiovascular disease, and developmental effects in children. The northeastern United States has particularly high natural arsenic concentrations in rock formations, but elevated levels exist in aquifers across the country.
Nitrate contamination is widespread in agricultural areas. At high concentrations, nitrate causes methemoglobinemia — "blue baby syndrome" — in infants, and emerging research links chronic exposure to thyroid disease and certain cancers. Unlike arsenic, nitrate in wells is primarily man-made, driven by fertilizer application and animal waste runoff.
Microbial contamination — bacteria, viruses, and parasites — was detected in roughly one-third of the 400 wells tested for biological contaminants. Coliform bacteria, including E. coli, can infiltrate wells through cracked casings, improper seals, or surface water intrusion during flooding. The gastrointestinal illness this causes is often attributed to "stomach bugs" rather than the water supply.
Man-made organic compounds — pesticides, solvents, and industrial chemicals — were actually detected in more than 60 percent of sampled wells. But concentrations rarely exceeded health benchmarks (less than 1 percent of wells). The detection itself, however, tells you something about how porous the boundary is between the surface and your aquifer.
PFAS — per- and polyfluoroalkyl substances, the "forever chemicals" — represent a newer and rapidly growing concern. Private wells near military bases, airports, industrial facilities, and even some agricultural land where biosolids were applied are increasingly found to contain PFAS compounds. Unlike public systems, which EPA now requires to test for and treat six PFAS compounds under the 2024 National Primary Drinking Water Regulation, private wells have no testing or treatment mandate.
The Regulatory Gap
Here's what makes private wells fundamentally different from public water:
| Public Water System | Private Well | |
|---|---|---|
| Federal regulation | Safe Drinking Water Act | None |
| Required testing | Regular, for 90+ contaminants | None |
| Treatment standards | Legally enforceable MCLs | None |
| Public notification | Required when violations occur | None |
| State oversight | All 50 states | Varies — often minimal |
The EPA's position is clear: "Private well owners are responsible for delivering safe drinking water to their households." That's it. The federal government provides educational resources and some mapping tools — including EPA's Interactive Private Domestic Well Map and data through DWMAPS — but no regulatory framework.
State-level regulation is a patchwork. According to the CDC, only 56 percent of local health departments regulate, inspect, or license private drinking water at all. Some states require testing at the time of well construction or property sale. A handful — New Jersey and New Hampshire among the most proactive — have established private well testing requirements. Most have nothing.
Georgia, for example — a state with significant rural private well usage — has construction standards for new wells but no requirement for ongoing water quality testing after the well is drilled. You could drink contaminated water for decades and never know unless you pay for testing yourself.
Contaminant Mixtures: The Understudied Risk
One of the most important findings from the USGS study deserves more attention than it receives: contaminants in private wells usually co-occurred as mixtures rather than alone.
This matters because toxicological risk assessments are almost always conducted on individual chemicals. The EPA sets a maximum contaminant level for arsenic. A separate MCL for nitrate. A separate one for lead. But your well isn't serving you one contaminant at a time — it may contain low levels of multiple contaminants simultaneously.
The total toxicity of a mixture can be greater than the sum of its parts. Two chemicals that are individually below health benchmarks may interact in ways that create a health risk neither would alone. This "cocktail effect" is poorly understood and almost entirely unstudied in the context of private well water.
Who's Most Vulnerable
Private well use isn't evenly distributed across the population. It's concentrated in rural areas, where homes are beyond the reach of municipal water infrastructure. The USGS has mapped these areas, and the pattern is clear: the people most likely to be drinking unregulated, untested water are in communities with the fewest resources to address contamination when it's found.
Children are disproportionately at risk. The American Academy of Pediatrics published a clinical report in 2023 specifically addressing drinking water from private wells and risks to children. Pediatric vulnerability to waterborne contaminants is heightened by developing organ systems, higher water consumption relative to body weight, and behaviors like hand-to-mouth contact.
Pregnant women face elevated risks from nitrate and certain microbial contaminants. Elderly residents and immunocompromised individuals are more susceptible to gastrointestinal illness from bacterial contamination.
The common thread: the people most vulnerable to contamination are the least likely to know about it.
What Actually Works
If you're on a private well, the fundamental problem is information. You can't address what you don't know about.
Annual testing is the single most important step. At minimum, the CDC and EPA recommend testing for:
- Total coliform bacteria and E. coli
- Nitrate
- Total dissolved solids
- pH
Testing for arsenic, lead, radon, and PFAS should be based on your region's known geological and industrial conditions. Your state geological survey or cooperative extension service can advise on area-specific contaminants.
Well maintenance is the second priority. Cracked casings, deteriorated grout seals, and damaged well caps are the primary pathways for surface contamination to reach groundwater. Annual visual inspection and periodic professional inspection can catch problems before they become health risks.
Treatment options exist for virtually every contaminant found in private wells. Reverse osmosis systems address arsenic, nitrate, and PFAS. UV disinfection handles microbial contamination. Activated carbon filtration reduces organic compounds. But treatment only works when you know what you're treating for — which circles back to testing.
The Gap Between Knowledge and Action
The information isn't hidden. The EPA, USGS, and CDC all publish clear guidance on private well testing. The data on contamination rates is publicly available. The health risks are well-documented.
The gap is between knowledge and action. Testing costs money — $50 to $200 for basic panels, $200 to $500+ for comprehensive analysis including PFAS. For many rural households, that's a significant expense with no mandate driving it. There's no bill, no reminder, no annual notice from a water utility telling you your water was tested and what they found. The default is silence.
And silence, when it comes to drinking water, means ignorance. Not safety.
The EPR Foundation's Protect People pillar focuses on water quality, contaminant exposure, and the regulatory gaps that leave communities unprotected. If you're on a private well, test your water. It's the single most important thing you can do.
Sources:
- U.S. Environmental Protection Agency. "Private Drinking Water Wells." Last updated March 24, 2026.
- DeSimone, L.A., Hamilton, P.A., and Gilliom, R.J. "Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991–2004." USGS Circular 1332 (2009).
- U.S. Geological Survey. "Domestic (Private) Supply Wells."
- U.S. Centers for Disease Control and Prevention. "Private Drinking Water and Public Health." Updated April 22, 2024.
- USGS New England Water Science Center. "Mapping and Characterizing the Arsenic Hazard in Private Well Water."
- American Academy of Pediatrics. "Drinking Water From Private Wells and Risks to Children." Pediatrics 151, no. 2 (2023): e2022060645.
- U.S. EPA. "Interactive Private Domestic Well Map."