Forest and Bird freshwater advocate Annabeth Cohen says the risk to human and environmental health is increasing along with the rise of nitrate levels. Photo: Supplied
Polluting nitrates are on the rise in Canterbury's drinking water and the risk maps the regional council is relying on are out of date, Forest and Bird says.
Using the council's own data, the environmental group created its own map, which it said showed an increasing number of private wells had nitrate levels above the safe standard for drinking water.
Forest and Bird freshwater advocate Annabeth Cohen said the last time the regional council, Environment Canterbury (ECan), updated its risk map for drinking water wells was 17 months ago.
She said analysis done on test results since then showed an increase in the number of wells where it was unsafe to drink the water due to nitrate levels, in Hurunui, Ashburton and possibly Selwyn.
"Environmental and human health is at a crisis point. So the situation is dire and getting worse. And ECan's data shows that the risk to human and environmental health is increasing."
Forest and Bird said they had been unable to get full access to ECan's data, but what they had seen showed some wells that had been classified as safe now exceeded safe limits.
The council was not due to update its risk map until the end of this year, but Ms Cohen said this should be done immediately in order to reassure residents reliant on the wells.
"Updating the risk map is a start. The major focus though should be on turning this dire situation around. And that has to do with cutting cow numbers, reducing fertiliser use and and seriously curbing the use of irrigation in the area."
Canterbury medical officer of health Alistair Humphrey said the risk maps were used by midwives to inform new mothers if their drinking water had dangerously high nitrate levels that might cause the potentially fatal blue baby syndrome.
He would prefer to wait until the council released its risk map at the end of the year before unnecessarily alarming new mothers.
However, he agreed that nitrate levels across the region were increasing.
Even with new measures being introduced to restrict cow numbers, the benefits would take a long time to show up due to the 10 to 20-year lag time between when cow urine hit the ground and when it showed up as nitrates in drinking water.
This meant things were going to get a lot worse before they got better, Mr Humphrey said.
"We have now more than 1.3 million dairy cattle in Canterbury alone. It's one of the densest dairy agro industrial plants in the world," he said.
Mr Humphrey recently spoke to the authors of a Danish study showing a link between very low nitrate levels and colorectal cancer, and said they were keen to see the same study carried out here.
"We should be looking to do our own studies in New Zealand of nitrates and colorectal cancer. For two important reasons. One, we have high and increasing levels of nitrates in this country. And two, we have relatively high rates of colorectal cancer."
ECan groundwater science manager Carl Hanson said Forest and Bird's analysis was not as thorough as the one the council did, and it wouldn't be until the end of the year before people could see if there was a heightened risk for private wells.
However, Mr Hanson said the overall trend did show increasing nitrate levels across the region.
"That is something that I'm afraid to say we expect to continue for a while yet. And it is the reason that we have spent on a lot of effort over the last number of years, developing limits on discharges from farming and other land use activities."
In reference to the Danish study, Mr Hanson said the levels attributed to an increased risk of cancer were often naturally occurring in waterways.