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Well Water Testing Guide

Private wells aren't regulated the way public water systems are, which means testing is entirely on the owner. Here's what to test for, how often, and where to get it done.

Why Private Well Owners Have to Test on Their Own

Public water systems are required to test regularly under the Safe Drinking Water Act, but that law doesn't cover private household wells. The EPA's private wells program puts the responsibility squarely on the homeowner: if your water comes from a private well, it's up to you to test it and, if needed, treat it. The EPA also notes that in a national assessment of private wells, 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, which is why testing isn't a one-time step you can skip after the well is drilled.

Test Annually for These Four

The EPA recommends testing your private well annually for total coliform bacteria, nitrates, total dissolved solids, and pH levels. These four are the baseline every well owner should be checking every year, regardless of region or well age.

• Total coliform bacteria. Coliform bacteria on their own usually aren't harmful, but their presence signals that surface water, septic effluent, or animal waste may be getting into your well, and that more dangerous organisms could be getting in the same way.
• Nitrates. Nitrate contamination typically comes from fertilizer, septic systems, or animal waste working into groundwater. The EPA's contaminant summary flags nitrate and nitrite specifically because high levels can cause methemoglobinemia, commonly called blue baby syndrome, in infants under six months, a risk serious enough that it can be fatal.
• Total dissolved solids (TDS). TDS is a rough measure of everything dissolved in the water, minerals, salts, and metals combined. The EPA's secondary standards guidance sets a non-enforceable benchmark of 500 mg/L for TDS, above which owners may start to notice hardness, staining, a salty taste, or colored water.
• pH. The EPA's secondary drinking water standards set a recommended pH range of 6.5 to 8.5. Water below 6.5 can have a bitter, metallic taste and become corrosive enough to leach lead or copper out of household plumbing; water above 8.5 can feel slippery, taste like soda, and leave mineral deposits.

What Counts as Hard Water

Hardness itself isn't a separate EPA-regulated parameter. Per EPA's secondary standards guidance, hardness shows up as one of the effects of elevated TDS, alongside staining, colored water, and a salty taste, rather than as its own numeric standard. In practice, a water test report will usually list hardness separately (often in grains per gallon or mg/L as calcium carbonate) even though it's driven by the same dissolved minerals that push TDS up. If your test comes back with high TDS, expect hardness to be part of the reason.

Test for Arsenic, Especially in Higher-Risk Regions

Arsenic doesn't show up on the EPA's core annual-test list, but it's one of the heavy metals the agency flags as a concern for private wells, noting it can cause acute and chronic toxicity, liver, kidney, and intestinal damage, and cancer. Arsenic occurs naturally in rock and soil and dissolves into groundwater over time, so risk depends heavily on local geology, not on anything the well owner did.

The Minnesota Department of Health recommends testing private wells for arsenic at least once, and says it "highly recommends taking protective action if the level of arsenic in your drinking water is above 10 µg/L," the same threshold the EPA uses as its maximum contaminant level for public systems. Minnesota's guidance also notes that consuming even low levels of arsenic over a long period is associated with diabetes and increased cancer risk in the bladder, lungs, liver, and other organs.

Arsenic exposure isn't evenly distributed. A USGS-supported well testing effort in Lycoming County, Pennsylvania found arsenic above the EPA's 10 micrograms-per-liter limit in 12% of the 75 wells sampled (one well measured 23.6 micrograms per liter). The same testing round found radon above the proposed 300 picocurie-per-liter standard in 67% of wells, and methane in 20% of wells, with two samples exceeding Pennsylvania's action level. That single-county snapshot is a reminder that the contaminants worth worrying about vary a lot by location, which is exactly why regional and situational testing matters as much as the annual baseline.

Test for Other Contaminants Based on What's Near Your Well

Beyond the four annual basics and arsenic, the EPA's guidance ties specific additional tests to specific situations near the well. A few examples from the EPA's private well protection guidance:

• Intensive agriculture nearby: test for nitrate, nitrite, pesticides, and coliform bacteria.
• Gas drilling operations nearby: test for chloride, sodium, barium, and strontium.
• Coal or other mining operations nearby: test for metals, pH, and corrosion.
• A dump, junkyard, or landfill nearby: test for volatile organic compounds, TDS, pH, sulfate, chloride, and metals.
• Household plumbing with lead pipes or lead solder: test for pH, lead, and copper.
• A water softener needed to treat hardness: test for manganese and iron.

The EPA's broader contaminant categories to be aware of include microorganisms (from sewage and animal waste), organic chemicals (from inks, dyes, pesticides, paints, solvents, and petroleum products), and radionuclides (associated with uranium mining, coal mining, and nuclear power production), each carrying its own health risks from gastrointestinal illness to kidney and liver damage to increased cancer risk. Because regional risk varies so much, check with your state or local health department for the contaminants known to be common in your specific area.

When to Test More Than Once a Year

Beyond the annual baseline, test right away if any of these apply:

• There's a known groundwater problem in your area.
• Conditions near the well change significantly, new construction, a new septic system, or new agricultural or industrial activity nearby.
• You've just replaced or repaired any part of the well system.
• Your water's taste, color, or smell changes.
• Small children, elderly adults, or someone pregnant or nursing lives in the house. These groups are more vulnerable to contaminants, so your local health or environmental department may recommend testing more often than once a year.

Where to Get Testing Done

Only use a laboratory that's certified to do drinking water testing. The EPA recommends contacting a state-certified laboratory or your local health department, which may offer private well testing for free. The Minnesota Department of Health's guidance echoes this and adds a practical tip: contact a few accredited labs before choosing one, since costs vary, and ask what container and sample-handling instructions they require before you collect your sample. If you're not sure who's certified in your state, your state health department or environmental agency's website will typically list accredited labs, and many maintain a searchable directory.

What to Do With the Results

If bacteria, nitrates, arsenic, or another contaminant comes back above the relevant limit, don't wait for the next annual test to act. Talk to your local health department about immediate steps (boiling water is not effective against nitrates or most chemical contaminants, so don't assume it's a universal fix), and consult a water treatment professional about a system sized for the specific contaminant you found. A well driller can also help rule out whether the problem is coming from the well construction itself, a cracked casing or a poorly sealed wellhead can let surface contamination in. See our guide to hiring a licensed well driller if you suspect the well itself needs attention, or our cost guide for what testing and treatment typically run.

Sourced from the EPA's Protect Your Home's Water guidance and Well Water Contaminants and Their Impacts page, the EPA's Secondary Drinking Water Standards guidance, the Minnesota Department of Health's well testing guidance, and a USGS-supported well testing study in Lycoming County, Pennsylvania. Testing recommendations vary by state and by local conditions; check with your state or local health department for guidance specific to your area.