Nitrite in well water: limits and risks for babies
The limit for nitrite is 1 mg/L as nitrogen in both the US and Ontario. Nitrite is a particular risk for babies under six months, so above the limit don't use the water for infant formula.
- US (EPA)
- 1 mg/L as nitrogen.
- Ontario
- 1 mg/L as nitrogen.
What it is
Nitrite forms from nitrate and from waste, so it usually comes from the same sources: fertilizer, manure and septic systems. It is usually much lower than nitrate. Finding nitrite can mean contamination is recent or close to the well.
What your number means
- Within limitsBelow 0.5 mg/L
Under the limit by a comfortable margin.
- Close to limit0.5 to 1 mg/L
Under the limit but more than halfway there. Retest within a year.
- Above limitAbove 1 mg/L
Use another source for drinking and cooking, contact your health department and retest to confirm.
What to do
- Check your nitrate result too, since the two usually travel together.
- Above the limit, use another water source for infants and anyone pregnant. Boiling makes it worse, not better.
- Ask your health department about likely sources near the well, and ask about reverse osmosis or ion exchange treatment.
How often to test
Every year if you have a baby at home or farm fields or a septic system nearby, otherwise every 3 to 5 years with nitrate.
Common questions
Is nitrite the same as nitrate?
No. They are related forms of nitrogen with separate limits: 10 mg/L for nitrate and 1 mg/L for nitrite, both measured as nitrogen. Nitrite is more toxic, but usually found at much lower levels.
Does boiling remove nitrite?
No. Boiling concentrates it as water evaporates. Use another source for infant formula until it's fixed.
Sources: EPA drinking water regulations; Ontario Drinking Water Quality Standards (O. Reg. 169/03). Limits checked November 2026.