Christchurch City Councillors will consider temporarily chlorinating the city's water when they meet this week.
The latest engineering assessments show some of the city's wells are vulnerable to contamination, particularly in heavy rainfall events.
This is because they're not sufficiently sealed to prevent surface groundwater entering.
Christchurch's drinking water is drawn from 156 wells, across 56 sites.
A programme is under way to get all wells upgraded by the end of the year but on Thursday councillors will decide whether to chlorinate the water in the meantime.
