From Thursday, the use of hoses, sprinklers and garden irrigation systems is permitted only on alternate days.
No water can be used outdoors on any day between 3pm and 9pm.
Several consecutive days of hot weather are forecast for the city, with little rain predicted in the long-term forecast, Christchurch City Council head of three waters and waste Helen Beaumont said.
This is expected to push up demand for water and put the city's water supply network under extreme pressure.
"When we get back-to-back days of high temperatures, we struggle to get water through the network fast enough to meet peak demand.
"That means there's a risk that we can't keep supplying drinking water at a constant flow and pressure, which can create problems in the network. There's also the risk that we won't have enough water in reserve to fight fires if we need to."
Under the restrictions, residents at odd-numbered addresses can water their gardens before 3pm or after 9pm on odd dates and residents at even-numbered addresses can water before 3pm or after 9pm on even dates.
Beaumont said the council is keeping a close watch on the weather and the city's water use.
"We are monitoring the weather forecasts and the city's water use on a daily basis. If we need to, we'll move to a higher level of restrictions."
Level 2 water restrictions were introduced last month in Akaroa, Duvauchelle and Takamatua on Banks Peninsula.
