Greenpeace says urgent action needs to be taken to reduce nitrate levels in drinking water, after a new study was released highlighting the link between dairying, nitrates and bowel cancer.
The report, overseen by Victoria and Otago universities, found up to 800,000 Kiwis may be exposed to potentially harmful levels of nitrates in their drinking water, which could increase their risk of bowel cancer.
The study has implications for the dairy industry, with cow urine and nitrogen fertiliser contributing to nitrate levels.
A map of New Zealand's cattle density and nitrate levels shows the higher the density of cows, the higher the level of nitrate pollution.
The research was overseen by Victoria and Otago universities and used a major Danish study on nitrate levels.
That study monitored 2.7 million people over 23 years and found a significant increase in bowel cancer risk at just 0.87mg/litre of nitrate-nitrogen per litre of water. At 2.1mg/litre there was a 15 percent increase.
New Zealand's drinking water standard is 11.3mg/l of nitrate-nitrogen - more than five times that.
Greenpeace campaigner Steve Abel says the new study is "disturbing, but not entirely unexpected".
"We've known for a long time that intensive dairying, driven by synthetic nitrogen fertiliser, is bad for our planet - causing climate change and contaminating rivers - this new report suggests it could be killing people too," he said on Monday.
"Where there are too many cows there are high rates of nitrate and where nitrate is high there are higher rates of bowel cancer."
Abel said industrial dairying was "effectively poisoning public and private water sources for profit and robbing us of something that belongs to everyone - our most fundamental resource - fresh water".
He said Greenpeace was calling on the Government to phase out synthetic nitrogen fertiliser and reduce cow stocking rates.