Nitrate in well water

Nitrate is one of the four things EPA recommends every private well owner test for every year. It has no taste, smell, or color, and it's one of the contaminants most likely to turn up in rural wells near farms, lawns, and septic systems.

Where it comes from

EPA lists chemical fertilizers, human sewage, and animal waste as the main sources of nitrate and nitrite. They reach wells through groundwater movement, surface water seeping in, and runoff. Shallow wells, dug and driven wells, and wells in sandy or gravelly soil are more exposed, because water reaches them quickly with little filtering. A septic drainfield upslope, or "upgradient," of a well adds to the risk.

Why it matters

Once swallowed, nitrate is converted to nitrite, which reduces the blood's ability to carry oxygen. EPA says high levels are most serious for infants. They can cause methemoglobinemia, or "blue baby syndrome," which can develop over a few days. Symptoms include shortness of breath and bluish skin. EPA warns that infants under six months who drink water with high nitrate levels can become seriously ill and die. Formula mixed with well water is the usual route, so a nitrate test is essential before using well water for a baby.

The standard

EPA's maximum contaminant level for public water is 10 mg/L of nitrate measured as nitrogen (nitrate-N), and 1 mg/L for nitrite as nitrogen. Some labs report nitrate as NO₃ rather than as N. Divide a result reported as NO₃ by about 4.43 to compare it with the 10 mg/L limit. A reading of 44 mg/L as NO₃ is about 10 mg/L as N. Our test reader uses the as-N limit.

A result well under 10 but rising from year to year is worth attention too. It suggests a source is affecting the well.

If your result is high

1. Don't boil the water to treat it. Boiling evaporates water and concentrates nitrate.
2. Use bottled water for infant formula, and for drinking and cooking if the level is above the standard, especially if anyone in the home is pregnant.
3. Retest to confirm, with a state-certified lab.
4. Look for the source. Check how close fertilized fields, lawns, livestock areas, and septic systems (including neighbors') are. Have your own septic system inspected. EPA lists high nitrate in wells as one sign of a failing system.
5. Talk to a water treatment professional about options. Reverse osmosis, anion exchange, and distillation are the usual approaches, and they need regular maintenance and follow-up testing.

Prevention

Keep fertilizer, manure, and pesticides well away from the wellhead, and follow application rates. Maintain the septic system, pumping and inspecting on schedule (see our pumping calculator). Make sure the well cap is sealed and surface water drains away from the casing. If you're drilling a new well, siting it upgradient of and away from septic systems and farmland, and drilling deeper into a protected aquifer, lowers the risk.

Who's most at risk

EPA and CDC both single out infants. CDC says high nitrate levels can make people, especially babies, sick. Groups to be most careful about:

• Infants under six months, particularly those fed formula mixed with well water.
• Pregnant people. CDC recommends testing your well when someone in the home becomes pregnant.
• Households with a new child. CDC recommends testing when a child starts living with you.

Older children and adults tolerate nitrate better, but a high reading still signals that other contaminants may be reaching the well.

Nitrate as a warning sign

CDC notes that if your water has high levels of nitrate, other harmful chemicals or germs may also be in it, because they often travel the same paths. A high nitrate result is a reason to:

• test for coliform bacteria if you haven't recently;
• ask your health department about pesticides if you're near farmland;
• check the septic system, since EPA lists high nitrate or coliform in drinking water wells among the signs of a failing system.

Common sources around a rural home

CDC lists animal waste, septic systems, wastewater, flooded sewers, polluted stormwater runoff, fertilizers, farm runoff and decaying plants. Around a typical property, check:

• Septic systems, yours and your neighbors', especially upslope of the well.
• Lawn and garden fertilizer applied near the wellhead.
• Livestock pens, barns and manure piles.
• Nearby crop fields, especially in spring after fertilizer application.
• Old or abandoned wells on the property that can act as a direct conduit to groundwater.

Seasonal swings

Nitrate levels can change through the year. They're often higher after spring snowmelt or heavy rain, when water carries fertilizer and manure into the ground. If your result is near the limit, testing at different times of year gives a better picture. Testing every spring is a good routine.

Treatment systems, briefly

• Reverse osmosis (RO): usually installed under the sink to treat drinking and cooking water. Needs periodic filter and membrane replacement.
• Anion exchange: treats the whole house. It works like a softener but uses resin selective for nitrate. Needs regular regeneration, and the right resin if sulfate is high.
• Distillation: treats small volumes and uses more energy.

Whatever you choose, test the treated water after installation and periodically after that.

Key takeaways

• Test for nitrate every year, and more often if an infant or pregnant person lives in the home.
• Don't boil high-nitrate water, because boiling concentrates it.
• A high result is a reason to look for sources and test for other contaminants.
• Use bottled water for infant formula until levels are confirmed safe.

Frequently asked questions

Can a water softener remove nitrate? A standard softener isn't designed for nitrate. Anion exchange systems with nitrate-selective resin are a different product.

Is showering in high-nitrate water safe? Nitrate is a concern when swallowed. Skin contact during bathing isn't the usual worry, but follow your health department's advice for your specific levels.

Will my health department test for nitrate? Many local or state health departments test for nitrate, often at low cost. CDC lists them as a good first contact.