Christchurch's water supply tested positive for E coli 14 times last year.
The positive results represent 0.2 percent of the 5500 samples taken.
The contamination occurred in shallow bores in the north-west of the city, the Christchurch City Council says.
It is working on improving the bores and hopes to have this done in the next two years.
Christchurch's untreated water, which comes from a series of bores around the city, is tested every day and results take 24 hours to come through.
The figures have been released in the wake of the Havelock North water contamination crisis.