A water test for arsenic is a laboratory job, not a strip you dip in a glass. Arsenic is colorless, tasteless and odorless, occurs naturally in bedrock across large parts of the country, and cannot be detected by any household sense, so the only way to know is to send a properly collected sample to an accredited lab.
Why arsenic needs a lab
Home strips exist for arsenic and they are far less reliable than the color-change kits people are used to for hardness or chlorine. The chemistry is difficult, the concentrations that matter are extremely small, and interference from iron and sulfide in well water makes field results unpredictable. An accredited laboratory uses instrument analysis that measures at the levels regulators care about and reports a defensible figure. That figure is what a treatment designer needs, and it is what a mortgage or real estate transaction will accept. A strip result is at best a prompt to order a real test.
Collecting the sample correctly
The lab sends a specific bottle, sometimes preserved, with instructions that are not optional. In general you take the sample from a cold tap that is plumbed ahead of any treatment equipment, run the water long enough to draw fresh water from the well or main rather than water that has been standing in the pipes, and avoid the aerator if the kit says to. Fill without rinsing a preserved bottle, cap it immediately, keep it cool and get it back inside the stated holding time. A sample taken after a softener or filter tells you about the equipment, not about the source.
The two forms and why they change the treatment
Arsenic exists in water in two forms, commonly written as arsenic three and arsenic five. Most treatment technologies, including adsorptive media, anion exchange and reverse osmosis, remove the five form far more readily than the three form. Groundwater under reducing conditions, which is common in wells, often carries the three form. That is why a serious test request includes speciation, or why a treatment designer will add an oxidation step ahead of the removal stage to convert everything to the more removable form. Ordering a total arsenic number alone can lead to a system that underperforms in service.
Who has to test and how often
If you are on a utility, arsenic is monitored for you and appears in the annual Consumer Confidence Report the EPA provides a finder for. If you are on a well, nobody is checking. The EPA notes that private wells are not federally regulated under the Safe Drinking Water Act, that around 15 percent of the US population relies on them, and that a USGS study of 2,100 private wells found about one in five carried at least one contaminant above a human-health benchmark. Test at purchase, after any well work, and periodically thereafter. Our well water testing guide covers building a sensible panel.
Questions people ask about water test for arsenic
Can I taste or smell arsenic in water?
No. Arsenic is colorless, odorless and tasteless at the concentrations that matter, which is exactly why laboratory testing is the only detection method.
Do home arsenic test strips work?
They are unreliable, especially in well water containing iron or sulfide. Treat a strip result as a reason to order a lab test, not as an answer.
Where should the sample be taken from?
A cold tap upstream of any treatment equipment, run long enough to draw fresh source water rather than water standing in the household pipes.
Will my softener remove arsenic?
A standard softener is not an arsenic treatment. Removal typically uses adsorptive media, anion exchange or reverse osmosis, often with an oxidation step first.