You can test your water for arsenic using a home test kit (around $15 to $30) or by sending a sample to a certified lab (typically $36 to $72). Lab testing is far more accurate and is the recommended approach if you rely on a private well, since the safety threshold is just 10 parts per billion, a concentration too low for most home kits to measure reliably.
The Safety Threshold You’re Testing Against
The EPA’s maximum contaminant level (MCL) for arsenic in drinking water is 10 parts per billion (ppb), which equals 0.010 milligrams per liter. The World Health Organization uses the same 10 ppb guideline, though it labels the number “provisional” because arsenic is difficult to remove from water completely. The previous U.S. standard was 50 ppb, five times higher, so older test results or kits calibrated to that threshold are outdated.
Public water systems are required to test for arsenic and treat it if levels exceed the MCL. Private wells have no such requirement. If your home is on well water, testing is entirely your responsibility.
Home Test Kits: Fast but Limited
Most consumer arsenic test kits use a method dating back to 1907. You mix a chemical reagent with your water sample inside a small chamber. The reaction produces arsine gas, which rises and contacts a test strip impregnated with mercuric bromide. The strip changes color depending on how much arsenic is present: a faint yellow suggests 10 to 50 ppb, brown indicates 50 to 100 ppb, and black means more than 100 ppb. You compare the strip to a color chart to estimate concentration.
The semi-quantitative steps on these kits are typically 0, 10, 30, 50, 70, 300, and 500 ppb. That sounds precise, but reliability at low concentrations is a known problem. In older kit designs where the gas passes over the strip rather than through it, contact between the gas and paper is poor, leading to low sensitivity and inconsistent readings. Newer designs force the gas through the paper and perform better, but distinguishing between 0 and 10 ppb by eye remains difficult for most people. If your water is close to the 10 ppb cutoff, a home kit may not give you a clear answer.
Home kits cost roughly $15 to $30 and deliver results in about 20 minutes. They’re useful as a screening tool, particularly if you suspect very high contamination. But if the result is anywhere near the safety limit, laboratory confirmation is essential.
Laboratory Testing: The Reliable Option
Certified labs use a technique called inductively coupled plasma mass spectrometry, which can detect arsenic at concentrations far below 1 ppb. This is the same method the EPA and FDA use for regulatory testing. The Wisconsin State Laboratory of Hygiene, for example, charges $36 for a standard arsenic test with results in about 10 business days, or $72 for a rush turnaround of two business days.
To find a certified lab near you, search your state’s department of health or environmental quality website for “certified drinking water laboratories.” Many state labs accept samples by mail, and some county health departments offer subsidized testing for private well owners.
Speciation Testing
If your total arsenic level comes back elevated, you may want speciation testing, which breaks down how much of the arsenic is in its two main inorganic forms. One form (trivalent, or As III) is more toxic than the other (pentavalent, or As V) because it interferes directly with protein function in your cells. The two forms also behave differently in water treatment systems: some filters remove one form far more effectively than the other. Knowing which type dominates in your water helps you choose the right filtration strategy. Speciation testing runs around $150 at a state lab and includes total, dissolved, trivalent, and pentavalent arsenic measurements.
How to Collect a Water Sample
Proper sample collection matters. A contaminated bottle, stagnant water, or splashing during collection can throw off results. Follow these steps:
- Use the lab’s container. Most labs provide or sell sterile sample bottles. If you’re using your own, make sure it’s a clean, uncontaminated container with no soap residue.
- Choose a cold water tap close to the well. A kitchen faucet works, but avoid taps with water softeners or filters in the line if you want to know what’s actually in your well water.
- Flush the line for 2 to 3 minutes. Let cold water run until the temperature stabilizes, which indicates you’re drawing fresh water from the well rather than water that’s been sitting in the pipes. Adjust the flow so it doesn’t splash against the sink or surrounding surfaces.
- Fill the bottle and cap it immediately. Leave no air gap unless the lab’s instructions say otherwise.
- Keep the sample cool. Place it in a cooler or refrigerator and deliver or ship it to the lab as quickly as possible, ideally within 24 hours.
Note that this flushed-water method differs from lead testing, which requires a “first draw” sample after water sits undisturbed for at least six hours. For arsenic, you want flushed water that represents what’s coming from the aquifer, not what’s leaching from your plumbing.
Understanding Your Results
Lab results for arsenic may be reported in micrograms per liter (µg/L) or milligrams per liter (mg/L). These two units trip people up because they differ by a factor of 1,000. One microgram per liter equals one part per billion. One milligram per liter equals one part per million. So 10 µg/L, 10 ppb, and 0.010 mg/L are all the same concentration: the EPA’s safety limit.
If your result is at or below 10 ppb, your water meets the federal standard. Levels between 5 and 10 ppb are legal but worth monitoring, since they’re close to the cutoff and arsenic concentrations in groundwater can shift over time. Above 10 ppb, you should stop drinking the water untreated and look into a filtration system designed for arsenic removal, such as reverse osmosis or specialized adsorptive media.
Long-term exposure to arsenic above the MCL is linked to gastrointestinal problems (nausea, vomiting, abdominal pain), numbness or burning in the hands and feet, and skin changes including dark spots and thickening on the palms and soles.
How Often to Retest
Arsenic levels in groundwater are not static. Changes in aquifer chemistry, water table depth, seasonal rainfall, and nearby land use can all shift concentrations. Research analyzing well data from multiple countries and aquifer types found a consistent recommendation: test your well every five years if your arsenic level is below half the MCL (below 5 ppb), and test every year if it’s at or above 5 ppb. That yearly schedule keeps the probability of unknowingly drinking water above the MCL below 5%.
If you’ve recently installed a treatment system, test more frequently at first to confirm the system is performing as expected. And any time you notice a change in your water’s taste, color, or odor, retest regardless of your usual schedule.