Testing your well water: what to test for, how often, and what it costs

The four tests, once a year

The CDC and the EPA give the same short list, in almost the same words. Test annually for total coliform bacteria, nitrate, total dissolved solids and pH, at a state certified laboratory.

That is the floor, not the whole picture. Both agencies say to ask your health department what else matters where you live, because the risks are local: arsenic in one county, radon in the next, nitrate wherever there is a lot of fertiliser or a lot of septic systems.

CDC, guidelines for testing well water, published 1 July 2024. EPA, protect your home's water, page updated 26 February 2026.

The six moments to test besides the annual one

The CDC lists these plainly, and they are the ones people skip:

• You hear there are problems with well water in your area.
• Something happened near the well: flooding, land disturbance, a nearby waste site.
• You replaced or repaired any part of the well system.
• The taste, the colour or the smell changed.
• Someone in the house becomes pregnant.
• A child comes to live with you.

The last two are on that list for one reason: nitrate. Infants under six months who drink water high in nitrate can develop methemoglobinemia, and the EPA says plainly that they can become seriously ill and die. It is the one contaminant on the annual list with an immediate, well documented consequence for a specific person in the house.

CDC, guidelines for testing well water, 1 July 2024. EPA, potential well water contaminants and their impacts, page updated 6 July 2026.

After a flood, the order matters

The sequence the EPA gives is inspect, disinfect, then sample. And the CDC adds the step that trips people up: after disinfecting the well, wait seven to ten days before collecting the sample, because the test is meaningless while chlorine is still in the system. Until the result comes back, boil vigorously for one minute or drink something else.

If you are treating water in the meantime, our treatment dose calculator gives the federal dose for the container you actually have, with the waiting time.

EPA, what to do to your private well after a flood, page updated 18 June 2026. CDC guidance on disinfecting wells after an emergency; we could not confirm the revision date of that CDC page.

Where to get it done, and what it costs

The official route is a laboratory certified by your state. The EPA does not keep a national list of laboratories; it keeps the list of state certification programmes, and you go from there to your state's list. Your local health department is the other route, and the EPA notes that some of them test private wells for free.

On price, be careful with what you read, including here. No federal agency publishes a typical cost. What exists are the price lists of public and university laboratories, which are real numbers for real tests:

So the annual four parameter test lands somewhere around 60 to 150 dollars at a public or university laboratory, and a wide panel with metals and volatile compounds runs from 200 to 450 and up. That range is our reading of those two price lists, not a figure published by any agency.

EPA, contact information for state certification programs, page updated 11 August 2026. Penn State AASL price list, read 17 September 2026; the page does not state an effective date. Wisconsin State Laboratory of Hygiene price list, effective 1 July 2026. EPA Safe Drinking Water Hotline: 1-800-426-4791.

How common is a problem, really

The honest answer includes a disagreement. The USGS national assessment of about 2,100 domestic wells found roughly 23 per cent had at least one contaminant above a level of health concern, with radon, arsenic, uranium, manganese and nitrate at the top. The EPA, summarising the same programme, says about one in five. Those are different slices of the same work, and we are not going to average them into a tidier number.

The finding that matters more than either percentage is this one: contaminants in well water usually do not arrive alone. They come as mixtures, which is why the annual panel exists instead of a single test for the thing you happen to worry about.

USGS, contamination in US private wells, page dated 6 June 2018, from the NAWQA assessment with data collected between 1991 and 2004. EPA, private drinking water wells, page updated 25 August 2026.

What the federal limits mean for you, which is less than you think

The numbers everyone quotes, 10 milligrams per litre for nitrate, 0.010 for arsenic, are Maximum Contaminant Levels set under the Safe Drinking Water Act. They apply to public water systems. They do not apply to your well. For a private well they are a yardstick you may choose to use, and nothing more: there is no federal requirement to meet them, and none to test at all.

Radon is the case that surprises people: there is no federal limit for radon in drinking water. A rule was proposed in 1999 and never finalised.

What that adds up to is covered in well water versus city water, which is the same subject from the other side.

EPA, National Primary Drinking Water Regulations, page updated 31 August 2026. The 1999 radon proposal is in the EPA archive.

Sources, with the date of each

• CDC, guidelines for testing well water, published 1 July 2024.
• EPA, protect your home's water, page updated 26 February 2026.
• EPA, what to do to your private well after a flood, page updated 18 June 2026.
• EPA, potential well water contaminants and their impacts, page updated 6 July 2026.
• EPA, state laboratory certification programmes, page updated 11 August 2026.
• EPA, National Primary Drinking Water Regulations, page updated 31 August 2026.
• USGS, contamination in US private wells, page dated 6 June 2018, data from 1991 to 2004.
• Penn State and Wisconsin State Laboratory of Hygiene price lists, read 17 September 2026.

What we did not state, because we could not confirm it: a per contaminant breakdown of the USGS percentages, the revision date of the CDC page on disinfecting a flooded well, and any federal figure for what a test costs.