Coromandel Town is under a boil water notice as tankers are being brought in to provide temporary assistance due to the town's water supply being undrinkable
A combination of dirty stormwater reaching the treatment plant, a power failure on Sunday night, and a leak in one of the chemical pipes caused the plant's clarifier to overload.
The clarifier is used to clean the water prior to it being treated through the filters.
The larger than usual volumes of very dirty water reaching the plant caused the clarifier to work at an increasingly slower pace, meaning less water has been produced and reservoir levels have also dropped.
"Our staff have been in touch with the local cafes and will continue to contact them to ascertain what specific assistance we can provide," said Thames-Coromandel District Council infrastructure manager Mohamed Imtiaz.