How to Test Water for Arsenic? | Lab vs. DIY Test Kits

Water is tested for arsenic by your own DIY colorimetric kit or an accredited lab, and only the lab gives a definitive reading.

Arsenic has no taste, no smell, and no color, so a contaminated well can stay hidden for years. The practical answer to how to test water for arsenic comes down to two routes: an accredited lab that measures the exact concentration, or a DIY colorimetric kit that screens a sample at home. Both are covered below with the exact steps, plus the mistakes that invalidate results.

Arsenic Water Testing Options: Lab Analysis Or A DIY Kit

You can test for arsenic two ways, and they answer different questions: an accredited lab produces a precise concentration, while a DIY kit gives a color-based screening result. The EPA’s home drinking water testing guidance is the federal starting point for consumers, pointing users to state programs and accredited labs. Dartmouth’s Arsenic and You project puts it plainly: a lab sample tells you how much arsenic is in the water, and that result should be confirmed with a second test.

The table below sums up how the two approaches differ.

EPA-approved analytical methods exist for this measurement.

How To Collect A Water Sample For Lab Testing

Collect the sample from the tap you drink from most often — usually the kitchen sink — and use a lab with an arsenic reporting limit no higher than 5 ppb.

1. Choose the tap you drink from most, typically the kitchen sink, and use the sample container the lab sends you.
2. Fill the container to the fill line and label it clearly.
3. Return the sample per the lab’s instructions. For an arsenic-only test, refrigeration and overnight shipping are not needed; other contaminants may require special storage and shipping.
4. Ask whether the lab is accredited to analyze drinking-water compliance samples — Dartmouth stresses this question, because accreditation is what makes the result trustworthy.
5. Ask for the arsenic reporting limit. Dartmouth warns that a 10 ppb reporting limit can return “not detected” when the water actually holds 9 ppb of arsenic.
6. When the report arrives, plan a confirmation test. Dartmouth recommends a second test to confirm the first result.

A solid lab report lists a precise arsenic concentration in ppb, not just “detected” or “not detected.”

How Do DIY Arsenic Test Kits Work?

A DIY arsenic kit screens a water sample by triggering a color change and matching it to a chart. It is a screening tool, not a lab-grade measurement.

1. Fill the reaction vessel to the volume the instructions specify — often 100 mL — with a freshwater sample.
2. Add the reagents the kit provides.
3. Wait the kit’s specified time. Common windows are 30–35 minutes or 10–12 minutes, and reading too early or too late can distort the result.
4. Compare the color to the chart. For best results, run the test at 22–28°C, and keep caps and test pads dry before use — moisture is a common cause of bad readings.

Color matching leaves room for judgment, so treat a kit as a first signal and let an accredited lab deliver the final word.

If you want a capable kit for a fast home check, our roundup of the best arsenic water test kits covers the models we’ve tested and how they compare.

The fastest honest path: run a DIY kit for a quick signal, then confirm anything it suggests with an accredited lab that reports at 5 ppb or lower. That combination gives you a screening result today and a defensible number when it counts.