Dairy farmers are being warned against using a border strip or flooding types of irrigation systems because of the risk to their health.
A groundwater study in South Canterbury has found that the risk of contracting e-coli and campylobacter from wells on dairy farms that use flooding irrigation is significantly higher than on those using spray irrigation systems.
It also found that the risk of contracting these diseases is higher during the irrigation season.
Environmental Science and Research scientist Dr Murray Close says he sampled wells less than 15 metres deep.
He says there is a 35% chance of getting sick from drinking water from a well on a dairy farm that uses flood irrigation.
There has been a massive increase in dairy farming in Canterbury over the past 15 years because of irrigation.
Nearly 15% of the country's dairy herds now reside there and it also has the largest average herd size per farm of more than 700 cows. The national average is 366.