Arsenic in drinking water is naturally occurring in many aquifers, dissolved out of the rock the well draws from, and it gives no taste, color or smell at the concentrations that matter. There is no way to know it is there without testing, and no household symptom that will prompt you to. That is the entire case for owning or commissioning a test.
Why private wells carry the risk
The EPA notes that private wells are not federally regulated under the Safe Drinking Water Act, so nobody tests them but the owner, and that around 15 percent of the US population, over 43 million people in more than 23 million households, rely on them. A USGS study of 2,100 private wells found about one in five carried at least one contaminant above a human health benchmark. On a municipal supply the utility monitors and reports; on a well the responsibility sits with you, and arsenic is one of the contaminants that a routine bacteria and nitrate test does not cover.
What a home kit can and cannot do
Home arsenic kits generate arsine gas from the sample and read the result on a treated strip against a color chart. Used carefully they are useful as a screen: they will tell you whether arsenic is essentially absent or clearly present. What they cannot give you is a defensible number near the regulatory threshold, nor the split between arsenic three and arsenic five, and that split decides the treatment. They are also sensitive to timing, temperature and sulfide interference, all of which push a reading the wrong way if the instructions are treated casually.
When to use a laboratory instead
Send the sample to a certified laboratory whenever a decision follows the result: a purchase, a sale, treatment design or anything involving an infant or a pregnancy. Use a lab too if a home screen shows any color at all, because the number matters at that point, and ask specifically for arsenic speciation so the design can be right. Arsenic five is removed readily by reverse osmosis, anion exchange and adsorptive media, while arsenic three usually needs oxidation first or it passes straight through. Our well water testing guide covers what else to test at the same time.
Sampling properly
A bad sample invalidates a good test. Take it from an unfiltered tap as close to the well as possible, so you measure the source rather than something a filter is currently masking, and remove the aerator. Run the tap until the water is cold and steady to draw fresh aquifer water rather than what stood in the pressure tank. Follow the kit or lab bottle instructions exactly on rinsing and headspace, and get the sample to a lab within the time it specifies. Retest periodically, since arsenic levels shift with pumping and season rather than staying fixed.
Questions people ask about arsenic test kit
Can I taste or smell arsenic in water?
No. It has no taste, color or odor at the concentrations that matter, so testing is the only way to know it is present.
Is a home kit good enough?
As a screen, yes. For any decision near the threshold, no. Home kits cannot give a defensible number or identify which form of arsenic is present.
Why does the form of arsenic matter?
Arsenic five is removed by reverse osmosis, anion exchange and adsorptive media. Arsenic three usually needs oxidation first or it passes through.
Where should I take the sample from?
An unfiltered tap close to the well, aerator removed, after running until the water is cold and steady so you sample the aquifer, not the pressure tank.