Many water supplies in Australia are derived from groundwater or bore water. Groundwater often can contain a number of chemical compounds. When nitrogen fertilizers are used to enrich soils, nitrates may be carried by rain, irrigation, and other surface waters through the soil into groundwater. Agricultural practices have been linked to elevated levels of nitrates in drinking water. Nitrates are very soluble in water and can move easily through the soil. Over time nitrates can accumulate in groundwater that may then be used as a drinking water supply. Elevated nitrate levels may suggest the possible presence of other contaminants such as disease-causing organisms, pesticides, or other inorganic and organic compounds that could cause health problems.
Infants less than three months of age are at risk from nitrate ingestion due to the conversion of the oxygen-carrying haemoglobin in their blood to an inert form known as methaemoglobin. This condition (methaemoglobinaemia) occurs when nitrate is consumed and converted to nitrite. The affected blood carries less oxygen than it should, turning blue and depriving the body of the oxygen it needs. Infants in the first three months of life are particularly susceptible to nitrite-induced methaemoglobinaemia because their stomach acid is not strong enough to stop the growth of bacteria that convert nitrate to nitrite.
The World Health Organization (WHO) and Australian drinking water guideline levels are 50 mg/L for nitrate (as NO3-) and 3 mg/L for nitrite (as NO2-). The guideline values are established to protect young infants from met haemoglobin formation, however, the guideline advises that water with a nitrate concentration of up to 100 mg-nitrate/L can be used by adults and children over 3 months of age without the risk of significant health effects (NHMRC, 2004). The WHO has also set a provisional guideline level for nitrite in drinking water of 0.2 mg/L for long-term exposure (WHO, 2008).
In Australia, nitrate concentrations in major public supplies of drinking water are typically below 0.15 mg/L, however, elevated nitrate concentrations (200-300 mg-nitrate/L) have been recorded in groundwater sourced for drinking in some rural areas. Nitrite is rapidly oxidized to nitrate in water and is rarely detected in well-oxygenated or chlorinated water (NHMRC, 2004).
Read the full Document Survey of Nitrates and Nitrites in Food and Beverages in Australia