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Nitrate in well water

NO₃

Measured in ppm as nitrogen · Updated 2026-09-15

This one is about health, not staining. Confirm any result with a certified laboratory and raise it with your county or state health department. Treatment choices here depend on details a web page cannot establish.

A genuine health standard rather than a staining threshold, and the population at risk is infants under six months. It is also a signal about the well itself, because nitrate is not naturally abundant in deep groundwater.

Why
The federal limit is 10 mg/L measured as nitrogen. Above it, the concern is methemoglobinemia in infants, which is why this is one of the few well water results that changes what a household should do today.
Watch out
Boiling makes it worse, not better. Water boiled to concentrate removes water and leaves the nitrate behind at a higher concentration. Confirm any result with a certified lab and speak to your health department.

Federal health standard

10 mg/L as nitrogen

An enforceable federal health standard for public systems. Private wells are not covered by it, which makes it a benchmark rather than a requirement.

What treats it

  • Reverse osmosis for well water

    Pushes water through a membrane fine enough to reject dissolved salts and most contaminants. Under the kitchen sink it is the most capable treatment available for water that is going to be drunk.

An enforceable health standard

Most numbers on a well water report are about staining, taste or equipment life. Deciding what to do about them is a spending decision with no deadline. Nitrate is an enforceable federal health standard for public water systems, set at 10 mg/L measured as nitrogen, and the reason it exists is methemoglobinemia in infants, where nitrate interferes with the blood’s ability to carry oxygen.

Private wells are outside the Safe Drinking Water Act, so nobody will require anything of a well owner on the basis of that number. It remains the benchmark the standard was built on, and a result above it changes what a household should do today rather than what it should buy this year.

The immediate steps are narrow: do not use the water for infant formula, do not boil it in the belief that this helps, and get the result confirmed by a certified laboratory. Then talk to a county or state health department, who deal with this regularly and will know the local picture.

Why boiling makes it worse

Boiling handles biological contamination by killing organisms. It does nothing to a dissolved mineral salt except remove some of the water surrounding it. Water boiled for ten minutes has less water and the same nitrate, which is to say more nitrate per glass than it started with.

The same logic applies to any dissolved contaminant that does not evaporate.

What the number says about the well

Nitrate is not naturally plentiful in deep groundwater. Where it turns up in quantity, something above ground is generally reaching the aquifer: fertiliser from a field, a septic system, a feedlot, or a wellhead that is not properly sealed.

That makes the result a piece of information about the well’s integrity as much as about the water’s chemistry, so treating it at the tap without asking how it arrived is an incomplete answer. Whatever path the nitrate found is available to bacteria and to whatever else is on the surface.

Test a well showing nitrate for bacteria at the same time, and have the casing, cap and surrounding drainage looked at.

Read next

  • Contaminant

    Coliform and E. coli in well water

    The one result that is about the well's physical condition rather than the water's chemistry. Bacteria in a well mean something is getting in, and disinfection treats the consequence rather than the cause.

  • Treatment

    Activated carbon filters for well water

    Adsorbs organic compounds, chlorine and the things that make water taste and smell wrong, on a bed of carbon with an enormous internal surface area. It is the polishing stage, and it is mandatory behind any chemical injection.

Not sure what is in your water yet?See which tests to order, thenplan the treatment from your results.

Questions

What do I do if my result is over 10?
Stop using it for infant formula and for children under six months immediately, and use bottled water for that purpose. Do not boil it, which concentrates rather than removes it. Have the result confirmed by a certified laboratory and contact your county or state health department, who will usually advise on retesting and on what the likely source is.
Where does it come from?
Fertiliser, animal waste and septic systems, mostly. Nitrate is not abundant in deep groundwater on its own, so finding it generally means surface water is reaching the aquifer. That is why the number matters beyond itself: whatever path the nitrate took is open to other things as well.
Will a softener or carbon filter remove it?
No to both. Nitrate passes straight through ion exchange softeners and activated carbon. Reverse osmosis and anion exchange are the recognised treatments, and point-of-use reverse osmosis at the kitchen tap is the usual residential arrangement.
Is it a problem for adults?
The standard is set with infants in mind, since they are the sensitive population. That does not make it irrelevant to everyone else, and the fact that surface contamination is reaching the well is a reason to look at the well itself rather than just to treat the water. This is a health department conversation.

Sources