Water restrictions are looming in the Garden City.

Christchurch City Council is expected to make a decision on Monday on whether to introduce water restrictions, akin to the hosing and sprinkler bans that are in force in Wellington.

Christchurch has had consistent temperatures in the 30s, no rain for more than 40 days, and water usage in the city remains high.

The local authority says the current high temperatures are making it difficult for water to pass through pipes and into reservoirs fast enough to meet demand.

On December 2 and 3, more than half a billion litres of water was used, the most used over a weekend in the city since January 2009.

On December 4, Christchurch used 254 million litres in total - the equivalent of 678 litres for every person in the city.

"If we can't keep the reservoirs filled, the pressure across the network drops," the council's head of three waters and waste, John Mackie, says.

"It also leaves us exposed in the event of a fire because having sufficient water in the reservoirs is essential for fire-fighting."

There has been one upside to the sudden heat.

The early heat wave has sent flowers at Christchurch's Botanic Garden into early bloom..

Guide Graham Chick said the gardens are at their most colourful right now, with roses popping up about three weeks ahead of schedule.

"All gardens are generally been about six weeks earlier than usual. We put that down to the fact we had a very wet winter and a very wet Spring and there are no recorded softs in the month of September."

Chick said they appear to be using sprinklers sensibly as the high temperatures hit.

The possibility of water restrictions come after other parts of the country, including Napier, have had to temporrily limit water due to the extreme weather.

- NZ Newswire, with content from Newstalk ZB