US EPA has established a maximum contaminant level (MCL) of 10 parts per million (ppm) for nitrates in drinking water. In my view this level is dangerously high. I will not drink water that contains even 3 ppm of nitrates. Several studies now show that nitrates may cause cancer at levels far below the EPA standards. People in agricultural communities or with well water may may be susceptable.
I view EPA MCL’s as guidelines that are heavily influenced by the political realities of imposing cost burdens on the cities that must comply with them. So for many contaminants I have my own tolerance standards. Nitrate is one of those.
Nitrates in drinking water may cause of cancer at levels below the EPA maximum contaminant level. Nitrate converts to nitrite in the stomach and the nitrites react with organic compounds to product N-Nitroso compounds. Many of these are known carcinogens. Bladder and stomach cancers are known to be caused by the N-Nitroso compounds.
Nitrates are particularly dangerous to young children or a developing fetus.
Update: January 2019
A new study released in January 2019 suggests a wider array of potential cancers due to nitrates.
You may see that study here:
To find out if you have nitrates in your drinking water check your local water report. Be sure to look at both the average levels and the range because nitrates will most likely spike during the summer months. For levels that reach 3 ppm or more I suggest that a reverse osmosis drinking water system is the best drinking water filter to remove them. Nitrates may also be removed from the whole house.