New research says 11,000 litres of water is needed to dilute the pollution from just one litre of dairy milk produced in Canterbury.
The study - published in the Australasian Journal of Environmental Management - says most of the groundwater near dairy pastures in the region is undrinkable due to high nitrate contamination.
Build up of nitrates there is projected to reach a concentration of 21.3mg per litre, nearly double the acceptable level for drinking water.
Victoria University of Wellington senior research fellow Dr Mike Joy was the reports lead author.
He spoke to Corin Dann.
