The short-term maximum acceptable value (MAV) for drinking water in NZ is 11.3 mg/L nitrate-N, which follows the accepted World Health Organization (WHO) Guideline Value. Risk maps have been produced which show that groundwater sites with nitrate concentrations that breach health standards are found in most regions, but are most common in dairying regions. In the Waikato, elevated nitrate concentrations have also been attributed to market gardening in areas where free-draining soils overlie a shallow water table.
However advice notes to the latest (4th edition) of WHO Drinking Water Guidelines make it clear that where water is microbiologically safe, water can be safely ingested (even by bottle fed infants) at concentrations up to 100 mg/L nitrate (equivalent to 22.6 mg/L NO3-N). In this paper we re-examine data from 3 regions, as well as a national data set, and determine new risk maps based on both E. coli (a faecal indicator bacteria) and nitrate concentration.