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.