Nitrates in Well Water

What nitrate is and how it gets into a well

Nitrate is a form of nitrogen. A little is natural, and Minnesota says natural levels in drinking water are usually below 3 mg/L. Higher levels almost always mean something on the surface is leaking down: lawn and crop fertilizer, septic systems, manure and feedlots.

Rain and irrigation water carry dissolved nitrate down through the soil to the water table. Shallow wells get hit hardest because there's less soil and rock to filter the water, and levels can swing with the seasons as fertilizer goes on and snow melts.

Minnesota lists the wells most at risk:

• Older wells, built before 1974
• Shallow wells, and dug wells with casings that aren't watertight
• Wells near septic systems or farm fields
• Wells in sand, karst or fractured rock
• Wells with cracked or leaking casings or fittings

If your well is on that list, have a licensed contractor look at the cap and casing before you spend money on treatment. A bad seal lets surface water straight in. See well inspection and well casing problems.

The limit, and the units that trip people up

EPA's maximum contaminant level is 10 mg/L for nitrate measured as nitrogen, and 1 mg/L for nitrite. Labs report it two ways. Nitrate-nitrogen (NO3-N) of 10 mg/L is the same water as nitrate (NO3) of 45 mg/L. Check which one your report uses before you panic or relax.

Minnesota adds a useful early warning: nitrate above 1 mg/L in well water suggests more testing may be a good idea, because other contaminants such as pesticides may be getting in too.

Health risks

Infants under six months are the main concern. EPA says babies who drink water above the limit could become seriously ill and, if untreated, may die, with symptoms including shortness of breath and blue-baby syndrome. That's methemoglobinemia, where the blood can't carry enough oxygen. Bottle-fed babies are at highest risk, and the bluish color of the lips and skin can be hard to spot.

Others to protect:

• Pregnant women. Penn State notes high-nitrate water has been linked to low birth weights.
• People with glucose-6-phosphate dehydrogenase (G6PD) deficiency or other metabolic conditions.

For most healthy adults, Penn State cites WHO and National Academy of Sciences findings that nitrate in drinking water poses no significant risk. Minnesota notes possible long-term links at lower levels that need more research.

How to test water for nitrates

Test every year. The CDC puts nitrate on its annual list with total coliform bacteria, total dissolved solids and pH. Test sooner if:

• someone in the house becomes pregnant, or a baby is on the way,
• the well floods or the land around it is disturbed,
• you repair or replace any part of the well system,
• the water's taste, color or smell changes.

Use a state-certified laboratory. Your county or state health department may run the test itself or give you a list of labs, and the lab will send the right bottle and instructions. Home test strips exist and can flag a problem, but before you buy treatment or decide a baby can drink the water, get a lab number.

Bacteria and nitrate often show up together because they come from the same places. Order a coliform test on the same visit; see coliform bacteria in well water and our full well water testing guide.

Treatment options

Nitrate dissolves easily, which makes it hard to remove, and the treatment is expensive to buy and keep up. Three methods work:

What doesn't work: boiling, ordinary filtration, disinfection and water softening. A regular softener or a carbon pitcher won't touch nitrate.

For most households we recommend reverse osmosis at the kitchen tap, because only the water you drink and cook with needs treating. Whole-house anion exchange is an option on farms or where livestock drink the water, since NC State says water above 25 mg/L of nitrate-nitrogen can harm animals. Either way, retest after install and on a schedule, because a membrane or resin bed that quits gives no warning.

Fixing the source beats treating forever. Minnesota recommends cutting nitrate sources on your property and having a licensed well contractor confirm the well is sound before you add treatment. NC State puts the ideal well site uphill and at least 100 feet from possible contamination.