The Christchurch City Council says its earthquake-damaged water supply network is not coping with the summer demand and water restrictions are likely.
More than half the South Island city's wells were damaged in the 7.1-magnitude quake on 4 September last year, and 10% are beyond repair.
Some 19km of water mains need replacing and three reservoirs also require repair.
The council's water and waste manager says although there is plenty of water in the city's aquifers, the damaged wells are struggling to replenish reservoirs when demand is high.
Mark Christison says water restrictions may be necessary within a week, unless demand drops by 10% and is warning people not to use too much water on their gardens.
Mr Christison expects it will take 18 months to get the city's wells back to their pre-quake condition.