Nitrate is one of the most common contaminants in American water, and one of the most important for new parents to understand. It comes mainly from fertilizer, manure, and septic systems washing into water sources — so it's especially common in farming areas and in private wells.
The classic risk: babies
High nitrate is dangerous for infants under six months. It interferes with the blood's ability to carry oxygen, causing a condition known as “blue baby syndrome” (methemoglobinemia). The most common route is formula mixed with high-nitrate water — which is exactly why this one matters so much for families with babies.
The newer concern: cancer, below the legal limit
The federal legal limit for nitrate — 10 mg/L — was set in 1962, based on that infant risk. But large studies since have linked nitrate to colorectal and other cancers at levels well below that limit. A study of millions of people in Denmark found increased risk starting around 0.9 mg/L; studies in Spain and Italy found similar signals. The legal number simply hasn't caught up with the science.
One myth worth killing: boiling water does not remove nitrate. It concentrates it.
What actually helps
Because boiling makes nitrate worse, the usual “just boil it” advice is exactly wrong here. Carbon filters generally don't remove nitrate either. What works is reverse osmosis or ion-exchange treatment.
What parents of infants should do
- Never mix formula with untested well water. If you're on a well and have an infant or are pregnant, test for nitrate before using it.
- Don't boil to “fix” nitrate — it raises the concentration.
- Use reverse osmosis if nitrate is elevated; confirm the system is rated to reduce it.
- Talk to your pediatrician if you have questions about your baby and water.