If you're on a private well, no utility monitors your water for you. The EPA recommends annual testing at minimum. State health departments frequently report that a significant share of private wells in agricultural and industrial regions exceed federal contaminant limits -- and most of those homeowners don't know it.
This isn't an abstract risk. The CDC estimates that 15 million US households rely on private wells, and surveys in states like Pennsylvania, Ohio, Minnesota, Iowa, and California have found double-digit percentages of wells with at least one contaminant exceeding federal limits.
Here's a practical guide to what to test for, when, how to do it, and what the results mean.
The Core Problem with Private Wells
Municipal water systems are required by law to test for dozens of regulated contaminants and publish annual Consumer Confidence Reports. If your city water has a problem, your utility is required to notify you.
Private wells are completely outside this system. The well is your property and your responsibility. If your well is contaminated with arsenic, nitrates, lead, bacteria, PFAS, or anything else -- no one will tell you unless you test.
The EPA's Safe Drinking Water Act explicitly does not apply to private wells serving fewer than 25 people. This isn't an oversight -- it reflects that regulating millions of individual private wells isn't practical. But it means the monitoring burden falls entirely on you.
The Annual Minimum: What Every Well Owner Should Test
Coliform bacteria (including E. coli) -- the baseline sanitation check. Coliform bacteria indicate fecal contamination -- meaning sewage, animal waste, or surface water is reaching your well. E. coli specifically indicates human or animal intestinal bacteria and is a more serious finding. This is the single most important annual test for any well owner.
Bacteria contamination doesn't produce a taste, smell, or visible change in water -- the only way to know is testing.
Nitrates -- particularly important if you have infants in the household, are pregnant, or are in an agricultural area. The EPA MCL is 10 ppm. Sources include fertilizer runoff, septic systems, and animal waste. Nitrates don't affect healthy adults at typical contaminated-well concentrations but cause infant methemoglobinemia (blue baby syndrome) at elevated levels.
pH -- affects corrosiveness and many other water characteristics. Well water outside the 6.5--8.5 range can be corrosive to plumbing (low pH) or scale-forming (high pH).
Total dissolved solids (TDS) -- a general indicator. High TDS suggests elevated mineral content; the nature of those minerals requires more specific testing. TDS itself isn't a regulated contaminant but flags water needing further investigation.
Hardness -- determines whether you need water softening. Also useful for understanding your overall mineral profile.
Extended Testing: What to Add Based on Your Location and Situation
The following should be tested at minimum once after moving in, and periodically thereafter based on local conditions:
Arsenic: Essential in Arizona, Nevada, New Mexico, parts of California, Texas, Maine, New Hampshire, and any area with volcanic or sulfide rock geology. The EPA MCL is 10 ppb; EWG's health guideline is 0.004 ppb. Arsenic is colorless, odorless, and tasteless. Many Arizona and Western well owners have arsenic above the MCL and don't know it.
Lead: If your well system or household plumbing includes lead components, or if you're in an older home with pre-1986 plumbing. Wells themselves don't typically contain lead -- it comes from the pump, pressure tank fittings, or interior plumbing.
PFAS: If you are within 10 miles of a military installation, a major industrial site, an airport, a firefighting training facility, or a landfill. PFAS are the most significant emerging contaminant in groundwater nationally. The 2024 EPA MCLs (4 ppt for PFOA/PFOS) mean many wells that were previously considered acceptable are now above the regulatory threshold.
Uranium and radium: Essential in Arizona, New Mexico, Colorado Plateau, parts of Wyoming, Idaho, and the Carolinas. Uranium is nephrotoxic (damages kidneys); radium is radioactive. Neither has a taste or smell.
Iron and manganese: Any well with reddish staining on fixtures (iron) or black staining (manganese), or any rotten egg smell (hydrogen sulfide). Iron above 0.3 mg/L causes staining and fouling of filters. Manganese above 0.05 mg/L causes black staining and has neurotoxic effects at higher levels.
Volatile organic compounds (VOCs): If you're near dry cleaners, gas stations, industrial facilities, or landfills. Common VOCs in groundwater include trichloroethylene (TCE), tetrachloroethylene (PCE), and benzene -- all carcinogens.
Pesticides and herbicides (atrazine, simazine): Agricultural areas, particularly in Iowa, Illinois, Indiana, Kansas, and other Corn Belt states where atrazine use is heavy. Atrazine is an endocrine disruptor detected in groundwater throughout agricultural regions.
Fluoride: Parts of Arizona, Texas, New Mexico, and the Great Plains have naturally high fluoride. Above 2 mg/L causes dental fluorosis; above 4 mg/L (the EPA MCL) causes more severe effects.
When to Test
Always test when: moving into a new property with a well, after any flooding or severe storm, after any well work or new construction near the well, or if taste, odor, or appearance changes.
Annually: Coliform bacteria and nitrates at minimum. More comprehensive if you're in an agricultural area or near industry.
Every 3--5 years (if prior results were clean): Full comprehensive panel including metals, VOCs, and your region-specific contaminants.
After contamination events: Spills, nearby chemical releases, or identified contamination in neighboring wells.
Testing Options: DIY vs. Mail-In vs. Professional
DIY Test Kits (Strip Tests, Colorimetric)
Single-use test strips or tablet-based kits that produce a color change you read visually against a chart. They can detect nitrates, pH, hardness, iron, chlorine, and hydrogen sulfide -- and provide basic lead and coliform screening.
Accuracy is low. A strip may show "nitrates present" but can't reliably distinguish 8 ppm from 20 ppm. Use for quick screening if you have visible water quality concerns (staining, smell, color). Not a substitute for certified lab testing.
Cost: $10--50 depending on the panel.
Mail-In Certified Lab Tests
You collect a water sample (following specific protocols), mail to a state-certified laboratory, and receive a detailed report of concentrations for each tested parameter. State-certified labs follow EPA-approved methods and produce defensible results you can act on.
Tap Score (Simple Water) -- various panels available from Essential Well ($129) to Premium Well ($280), plus specialized PFAS, VOC, and arsenic panels. Sends collection kit with detailed instructions; provides plain-language explanations and filter recommendations alongside results. The Premium Well panel covers 100+ contaminants including metals, nitrates, bacteria, VOCs, PFAS, and radiologicals.
National Testing Laboratories (NTL) -- one of the most established certified mail-in labs. Drinkwater Metals ($80), Drinkwater Check ($140), and comprehensive panels up to ~$350. Less consumer-focused presentation than Tap Score but rigorous lab results.
State health department labs -- many state health departments offer subsidized or free testing, particularly for coliform, nitrates, and arsenic. Check your state health department's private well program first -- you may get basic testing for $0--$30. Coverage varies widely by state.
Collection protocol matters: Following the instructions precisely -- using the provided sample bottles, the right flush time before sampling, not touching the inside of the bottle -- is essential. An improperly collected sample produces an invalid result.
Professional Well Inspection
A licensed well contractor or water treatment professional can test your water, interpret results, and recommend treatment in one visit. More expensive ($200--$500+ depending on region and panel), but appropriate for new home purchases, complex contamination situations, or when you want in-person guidance.
For new home purchases specifically: a comprehensive well inspection is standard in many rural real estate transactions and should be included in your due diligence. Ensure the inspection includes testing, not just visual inspection of well components.
Reading Your Results: What the Numbers Mean
The key thresholds to know: for nitrates, the EPA MCL is 10 ppm -- action required for infants and pregnant residents above this level. For arsenic, the EPA MCL is 10 ppb, though EWG recommends action at any detectable level if children are present. For lead, the EPA action level is 15 ppb, but any detection warrants action if children are present. For PFOA and PFOS, the 2024 EPA MCL is 4 ppt -- at or above this level compliance is required. For E. coli, any detection means boil water immediately with no safe threshold. For iron, 0.3 mg/L is the EPA secondary (non-enforceable) standard -- above this level causes staining and filter fouling. For uranium, 30 µg/L is the EPA MCL -- any detection warrants treatment consideration.
A note on EWG guidelines vs. EPA MCLs: EWG guidelines are derived from health-risk-based calculations at a one-in-one-million cancer risk level -- far more conservative than federal MCLs which balance risk against treatment cost. A well result between the EWG guideline and the EPA MCL is not an emergency but warrants treatment consideration, especially for pregnant residents and young children.
What to Do if You Find a Problem
Bacteria (E. coli detected): Boil all water for drinking and cooking immediately. Shock-chlorinate your well (your county extension office or health department can provide instructions). Retest. If the problem recurs, investigate for structural issues or contamination source.
Nitrates above 10 ppm (with infants or pregnancy): Use bottled water or RO-filtered water for infants and pregnant residents immediately. Do not use well water for infant formula. RO filtration is the standard home treatment. Investigate source (upgradient agriculture, failing septic system).
Arsenic above 10 ppb: Install under-sink RO for drinking and cooking water. Test children for blood arsenic levels if exposure has been extended. Notify state health department -- some states have programs to assist with treatment.
PFAS above 4 ppt: Under-sink RO is the standard home treatment. Notify your state environmental agency -- you may be eligible for assistance or remediation funding, particularly if near a military base or industrial facility.
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Sources: EPA: Private Drinking Water Wells · CDC: Private Ground Water Wells · NSF: Water Filter Certification · EWG: What's in Your Water · USGS: Groundwater Quality in Principal Aquifers of the United States