Papanui-Innes Community Board member Emma Norrish said Christchurch City Council has added chlorine to the Grampian St water supply pump station while it carries out age-testing of the groundwater.
Results from the latest batch of groundwater samples at one of the wells showed water younger than a year old may be present.
This indicated that it may still contain bacteria and viruses, which may present a risk to public health if left untreated, said Norrish.
“There has not been any E. coli detected in the groundwater at Grampian Pump Station, but the wells are being chlorinated as a precautionary measure.”
The testing will finish by the end of June, when the chlorine is also due to be removed.