Arsenic Water Testing: What Your Well Report Means

If your well has elevated arsenic—especially above 10 micrograms per liter—or you suspect harmful contamination, switch immediately to bottled water or another appropriate safe source for drinking, cooking, making ice, and preparing infant formula. Do not wait for a repeat sample or treatment quote before reducing exposure. Contact your health department for advice. Boiling does not remove arsenic and can concentrate it as water evaporates. CDC treatment guidance; Minnesota Department of Health arsenic guidance

What an arsenic test can tell you

You cannot see, smell, or taste arsenic in water. It can dissolve into groundwater from natural deposits, and levels can differ between nearby wells. Your neighbor’s report cannot establish your well’s arsenic level. MDH

Order a laboratory test that explicitly includes arsenic. A bacteria result, pH reading, or total dissolved solids measurement does not answer that question. Likewise, an arsenic-only result says nothing about contaminants the laboratory did not test. Use the well water testing guide to plan the rest of your testing. If you are still choosing between a certified lab panel, kit, or meter, start with the well water tester guide.

Order the right laboratory test

Use a state-certified drinking water laboratory. EPA provides links to state certification programs, and your health department can help locate a laboratory. Confirm that its current certification covers arsenic analysis for your state; a general accreditation statement or use of an EPA method alone is not that confirmation. EPA laboratory guidance; CDC testing guidance

Before ordering, ask:

• Does this test specifically include arsenic?
• What reporting limit and units will appear on the report? Can it measure below 10 µg/L?
• Which tap should I sample, and should the sample represent untreated water or water after treatment?
• What containers, collection instructions, delivery deadline, and shipping arrangements apply?
• If this is for a property transaction, will the laboratory and collection procedure satisfy the applicable requirements?

Get the laboratory’s containers and instructions before collecting water. Follow its directions for sample handling; do not substitute a household bottle or a generic online sampling procedure. MDH recommends obtaining containers and instructions directly from an accredited laboratory. MDH

If treatment is already installed, tell the laboratory. An untreated sample and a treated drinking-tap sample answer different questions. Ask whether you need both, and label each sample location clearly. For a home purchase, coordinate testing with the broader well water inspection.

Read the number, units, and reporting limit together

EPA’s arsenic maximum contaminant level, or MCL, for public water systems is:

10 µg/L = 10 ppb = 0.010 mg/L.

The maximum contaminant level goal, or MCLG, is zero. The MCL is an enforceable public-system standard that accounts for treatment feasibility and cost; the MCLG is a non-enforceable health goal. Federal public-system drinking water rules do not apply to private wells. For a homeowner, 10 µg/L is a comparison benchmark, not a federal private-well requirement or a boundary below which risk disappears. EPA drinking water regulations; CDC

Report finding	Interpretation and next step
Not detected, ND, or a less-than result	The laboratory did not report arsenic above the stated detection or reporting threshold. This does not prove zero arsenic. Ask the lab to explain the threshold if it is missing or unclear.
Detected below 10 µg/L	Below the public-system MCL, but long-term exposure can still carry risk. Discuss exposure reduction with your health department.
At or near 10 µg/L	At or close to the benchmark. Ask the laboratory about rounding and uncertainty, and discuss protective water choices and follow-up testing with your health department.
Above 10 µg/L	Switch drinking and cooking water now. Arrange health-department guidance and any recommended confirmation testing while using the alternative source.

MDH recommends considering treatment or a different drinking water source whenever arsenic is detected, and strongly recommends action above 10 µg/L. It also explains that long-term consumption below the MCL can increase cancer risk. MDH

Keep the complete report, including the sample date, location, units, reporting limit, and any laboratory comments. A repeat test can help resolve questions, but it should not postpone protective action after an elevated result.

Does arsenic mean you must stop bathing?

Arsenic guidance differs from advice for unknown chemical contamination. MDH says skin does not readily absorb arsenic and permits uses such as showering, bathing, and washing clothes, with an exception when arsenic exceeds 500 µg/L. This does not make the water suitable for drinking. Above that level, obtain specific water-use advice from your health department. MDH

Do not apply that arsenic-specific guidance to a flooded well, suspected fuel contamination, or other unidentified chemicals. Those situations require separate advice. CDC treatment guidance

Choose treatment and verify the result

MDH lists reverse osmosis, distillation, adsorptive media, anion exchange, and certain oxidation-and-filtration systems as arsenic-reduction options. Conventional water softeners and activated carbon filters alone do not remove arsenic. A treatment specialist should match the equipment to your report and household needs. MDH

Before accepting a proposal, request written answers about:

• Arsenic reduction: Does the exact model’s independent certification cover arsenic reduction, and under what water conditions and limitations?
• Suitability: Is your measured concentration within its operating conditions? Does the arsenic form require further testing or pretreatment?
• Coverage: Which taps and appliances will receive treated water? How will you supply all drinking and cooking uses?
• Upkeep: What maintenance, replacement parts, and service does the manufacturer require?
• Verification: Where and when will treated water be sampled, and what happens if the result remains elevated?

MDH recommends independently certified equipment, maintenance following the manufacturer’s instructions, and periodic testing of treated water. CDC advises testing after treatment to confirm that it worked before resuming use. Continue your alternative drinking-water arrangement until results support that change. An acceptable arsenic result does not establish that other contaminants have been removed. MDH; CDC

Set a retesting plan for your well

Minnesota’s advice is regional: MDH recommends an arsenic test beyond the initial construction test. If arsenic was detected in a new well, it suggests considering another test about six months after construction, because levels can change during those early months. That is not a nationwide six-month testing schedule. MDH

Ask your state or local health department for an arsenic schedule based on your results, local conditions, and treatment. Our state resources guide can help you find the appropriate program.

Separately, CDC recommends annual testing for total coliform bacteria, nitrate, total dissolved solids, and pH. It also recommends testing after well repairs, flooding or other nearby problems, local contamination notices, and changes in taste, color, or smell. Ask which additional contaminants each event warrants testing for; arsenic has no sensory warning. CDC testing guidance