How to Test for Arsenic in Well Water (And What Your Results Mean)

Arsenic has no taste, no smell and no color, so the only way to know whether it is in your well is to send a water sample to a lab. People ask me whether the arsenic tests at Lowe's and Home Depot are good enough. When it comes to arsenic, get a lab test.

The well water test kit we sell is $199. It ships to you, you fill the bottles following the instructions, and you mail the sample back in the prepaid envelope. Once the lab receives it, you get your results by email within 5 business days. The same report gives you the arsenic number and the pH, iron and hardness that decide which arsenic filter will work on your water.

Which arsenic test should I order?

For a well, order a lab test that reports arsenic plus your pH, iron and hardness, because you need all four numbers to pick an arsenic filter. An arsenic filter works on water that already has the iron and hardness taken out, and one sample gives you all of those numbers.

Whichever lab you use, check its reporting limit for arsenic. Dartmouth's arsenic researchers say it should be no more than 5 ppb, because a lab with a 10 ppb limit can report 9 ppb as "not detected." On the tests my customers get back from our kit, the arsenic reporting limit runs from 0.5 to 2 ppb.

I tell people we don't want to give advice unless they have an accurate water test we can look at, and that is why we sell tests. If your county tests wells, that number is still worth having; Minnesota's health department suggests asking your county environmental or public health office whether it tests wells.

Are hardware-store arsenic tests good enough?

A store arsenic kit like the ones at Lowe's and Home Depot is a rough screen, not a number you can buy a filter on. The kits work by turning any arsenic in the sample into a gas that colors a test strip in the cap, and you match the strip to a printed chart in 7 to 14 minutes.

The charts on the Ascel and ITS Quick kits step from 0 to 5 to 10 to 20 ppb. A strip that lands between two blocks leaves you guessing on the side of the line that matters, 5 ppb in New Jersey and New Hampshire and 10 ppb for the EPA. The strip also reads arsenic III and arsenic V together, and it tells you nothing about the pH, iron and hardness that pick the filter.

If you already have a strip result that showed color, take it as the reason to order the lab test, not as the answer.

How to take an arsenic water sample

Use the lab's own bottles, fill them at the right tap, and follow the lab's directions exactly. Particles and fine sediment in a sample can throw arsenic results off, and samples from the house plumbing carry less of it.

1. Use the bottles the lab sends

   The lab provides the sampling kit and its directions. Wisconsin's DNR says it is very important to follow them, and Dartmouth's arsenic researchers say the same. Don't pour the sample into a jar of your own.

2. Choose which tap to test

   To test the well itself, fill the bottles at a tap before any filter or softener. To test what you drink, use the tap you drink from most, which for most homes is the kitchen sink. If you have equipment, note which tap you used: when someone sends me a report, I ask where the water came from and whether it was before the equipment.

   

3. Fill the bottles at a house tap

   A U.S. Geological Survey and Minnesota health department study found arsenic results were most reliable when the sample came from household plumbing, not the drill rig's pump, and when a new well was sampled several months after it was built. On a brand-new well, test before you drink it and again a few months later.

4. Follow the return instructions on the box

   For an arsenic-only test, Dartmouth says you don't need to refrigerate the sample or ship it overnight. Our kit also carries a bacteria test, so follow its shipping directions and use the prepaid envelope.

5. Retest a high arsenic result

   Dartmouth suggests a second test to confirm your result. If the first one comes back over a limit, a second sample from the same tap tells you the number is real before you spend money on a filter.

Reading the arsenic number on your report

My customers' lab reports give arsenic in ppm. Multiply by 1,000 to get ppb, so 0.010 on the report means 10 ppb, the EPA limit. Ppm is the same as mg/L. A report from another lab may print ppb or µg/L instead, and those two are the same number.

What to do at each arsenic level, and what to drink until the water is treated, is in my arsenic guide.

Your arsenic result is back

Text Aidan your lab report

Send a photo of the whole report, not just the arsenic line. Aidan will take a look and make a recommendation.

Text Aidan443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.

Do I need the arsenic speciation test?

The speciation test tells you which type of arsenic you have, and whether your filter needs an extra step for it. If your report shows no arsenic, there is nothing to split. The $199 well water test reports total arsenic. The $519 arsenic speciation test splits that total into arsenite (arsenic III) and arsenate (arsenic V).

People call me with a report that just says total arsenic and ask what filter to buy. I tell them to buy a filter that removes both types. The split tells you whether your arsenic III needs an extra step ahead of the filter; that step is explained under arsenic III and arsenic V.

How often to test for arsenic

Test every well for arsenic at least once, then every 3 to 5 years. Arsenic varies from well to well, even within a small area, so a neighbor's clean result says nothing about yours.

• A new well: before you first drink it, and again a few months after it was built.
• No arsenic filter: every 3 to 5 years, the schedule Dartmouth's arsenic researchers give.
• With our arsenic filter: a lab test every 1 to 2 years from a tap after the filter. When arsenic starts coming back into the water, it's time to rebed the filter.

Testing for arsenic when buying a home

Some states, towns and mortgage lenders require a water test before a home with a well is sold, but those required tests don't always include arsenic. Ask the lender or the town which lab they accept and who has to take the sample before you order anything, and if arsenic isn't on their list, test for it yourself.

If you are looking at homes in a high-arsenic area, see which states have the most arsenic.

Frequently asked questions