Drinking water normally supplies only about 1% of one’s dally nitrate intake; vegetables provide most of the rest.  But some waters, usually from private wells in rural areas, contain many times the normal concentration.  The EPA nitrate standard is 10 parts per million (ppm).

High nitrate levels usually stem from agricultural activities.  Chemical fertilizers and manure from animal feed lots are particularly rich sources of nitrogen compounds, which are converted to nitrates in the soil.  Wastes leaking from septic tanks also add nitrate to groundwater.

Babies less than six months old may become seriously ill from drinking water high in nitrate.  The main threat to infants arises from formula mixed with nitrate-rich water.  Bacteria in infants' digestive tracts convert the relatively harmless nitrate to nitrite. Nitrite in turn combines with some of the hemoglobin in the blood to form a compound called methemoglobin, which cannot transport oxygen.  The resulting condition, methemoglobinemia, deprives vital organs of oxygen.

High nitrate levels may signal that other contaminants such as agricultural pesticides or bacteria and viruses from septic tanks are also present.  Some state health departments test private wells free. 

Distillers and reverse-osmosis units remove nitrate.  Digging a deeper well to an uncontaminated water source is another alternative.