Te Wai Pounamu / South Island

Only 1% of domestic wells mapped were in areas predicted to have nitrate concentrations below 1mg/L and almost half (49%) were in areas predicted to have concentrations within a range of 3.5 to 8.5mg/L, with a further 5% predicted to exceed 8.5mg/L, with some of these above 11.3mg/L.

The maximum allowable nitrate in drinking water is 11.3mg/L, but the National College of Midwives has warned pregnant women about levels exceeding 5mg/L risking preterm birth and low birthweights and public health academics have said levels below this may be a concern, including as a cause of colorectal cancer.

Ms Prickett said any level above 3.5mg/L was indicative of "serious degradation of environmental health let alone public health".