24 Jun 2019

Dairy farming and the water we drink

From Christchurch Dilemmas, 8:49 am on 24 June 2019

Dr Alistair Humphrey has a dire warning for our descendants and future users of Canterbury’s world-renowned drinking water, “pollution could render it undrinkable in 100 years.”

In the latest Frank Film episode, Dr Humphrey warns of the risk of nitrate contamination in Christchurch’s public water supply.

Speaking as the region’s Medical Officer of Health, Dr Humphrey assures residents their drinking water is currently safe to consume. His fear is for the future, and a predicted nitrate influx.

“Modelling from Environment Canterbury shows that nitrates on the north side of the Waimakariri River are flowing underneath that river towards the Christchurch urban drinking water supply,” says Humphrey. “There is a 75 perrcent chance that nitrate levels will increase significantly in the urban water supply in the next century.”

Christchurch’s alpine-fed, aquifer-purified water system is unique in New Zealand and, according to river engineer, Rob Blakely, there are few systems like it in the world.

“The fact that it comes out of the mountains, the snow covered mountains, and it flows across these wonderful plains with lots and lots of layers of gravel, hundreds if not thousands of feet deep.” says Blakely.

“When we draw water out of the aquifers of this river we’re getting the most beautiful, pristine water you could ever imagine. We need to be very careful that the water flowing into this river system is kept clean.”

Easier said than done, with a 1.3 million dairy cattle now grazing the Canterbury plains.

“Nitrogen is applied to improve poor quality soils,” explains Humphrey. “Cows excrete nitrogen as nitrate onto the paddock and into our aquifers.”

He warns that nitrates are already showing up in shallow, private bores throughout Canterbury and at levels above the World Health Organisation’s maximum allowable value of 11.3 mg per litre.

Water filter retailer, Sue Kelly, says reverse osmosis filters, imported from the United States and costing over $1200 NZD, remove nitrates from drinking water. She says hundreds of the under-bench units have been sold, and since a Danish study was released public awareness has grown further.

The study of 2.7 million people, found a link between nitrates in drinking water and incidence of bowel cancer.

Dr Humphrey has scrutinised the research, and says “the study accounted for all those other variables that may also give rise to bowel cancer, nonetheless it showed that nitrates in drinking water are a considerable contributor to this deadly and debilitating disease.”

He’d like to see the study replicated in New Zealand.

He’d also like to see a concerted effort to reduce cow numbers in Canterbury.

Explore more Frank stories here.