A freshwater scientist says Canterbury's water isn't safe to drink.
Canterbury Medical Officer of Health Dr Alistair Humphrey has called for urgent research into the levels of nitrates in the region's drinking water.
A Danish study found a correlation between nitrate in drinking water, and colorectal cancers.
Freshwater ecologist, Doctor Mike Joy, says increasing levels of nitrate are very concerning.
He told Chris Lynch he was born and bred in Canterbury, but if he was living there now he wouldn't take the risk of drinking the water supply.
Joy says he's sampled many rural Canterbury water supplies that are way above the increased level for cancer risk.