The maximum acceptable concentration of nitrates in drinking water is 10 mg/L as nitrogen. Nitrates are present in water (particularly ground water) as a result of decay of plant or animal material, the use of agricultural fertilizers, domestic sewage or treated wastewater contamination, or geological formations containing soluble nitrogen compounds. There is a risk that babies and small children may suffer blood related problems (methaemoglobinaemia) with excess nitrate intake.

Nitrate poisoning (methaemoglobinaemia) from drinking water appears to be restricted to susceptible infants. Most water-related cases have been associated with the use of water containing more than 10 mg/L nitrate as nitrogen. In Canada, there have been no reported cases where nitrate was consistently less than the maximum acceptable concentration. Where both nitrate and nitrite are present, the total combined concentration should not exceed 10 mg/L. In areas where the nitrate content of water is known to exceed the maximum, the public should be informed by the appropriate health authority of the potential dangers of using the water for infants.