Hundreds of thousands of people in the South Island are potentially being exposed to bacteria and parasites in their drinking water.
Regulator Taumata Arowai has singled out 27 councils without protozoa barriers on their supplies.
Christchurch City Council, Queenstown Lakes District Council, Waimakiriri District Council and Grey District Council are the worst offenders on a population basis.
Almost 170,000 people are at risk in the Garden City alone.
Samantha Gee has more.
