Thousands of earthquakes over the past eight months appear not to have significantly affected the quality of Christchurch's drinking water.

The Environment Canterbury (ECan) study of 35 wells around the city also showed no evidence of changes in groundwater flow patterns since September.

ECan director of investigations and monitoring Ken Taylor said it was pleasing to find the water quality in Christchurch's aquifers was similar to the quality before the quakes.

The water quality study took 21 measurements, including water acidity, temperature and the quantity of dissolved oxygen as well as the level of several salts and minerals.

Of the 35 wells, only seven had been damaged by quakes.

Four wells in the city's east had damage to the pump and/or wellhead, two were silted up and one appeared to have had an electrical fault, Taylor said.

Christchurch City Council testing found less than 1 per cent of 2500 samples had E coli contamination, which was being treated by chlorination.

"Shallow groundwater in some areas may have been contaminated by breakages in wastewater pipes, but there is very little risk of bacterial contamination to the deeper aquifers where drinking water is drawn from," Taylor said.

Fifteen wells showed no significant change in water quality.