But even though the city uses more water in hot weather, Icon Water says it would take conditions worse than the "millennium drought" for the water provider to consider introducing water restrictions.

Temperatures are set to hit 40 degrees or above three days in a row this week, 12 degrees above the average maximum, part of a string of hot summer weather that has seen dam levels in the ACT drop.

However, the water supply remains very secure.

The Bureau of Meteorology has forecast heatwave conditions until the weekend, with some relief expected on Sunday when temperatures drop closer to the January average of 28 degrees.

Bureau meteorologist Elli Blandford said a slow-moving high pressure system and an inland trough was acting to bring warm air from central Australia through NSW into the ACT.

"Because of the stationary high pressure system in the Tasman Sea, it's blocking fronts coming through that normally cool things from the south," she said.

"There should be some relief coming towards the end of the week."

Last year was the warmest on record for maximum temperatures in Canberra and water usage in the capital has increased year on year since 2015.

Combined storage levels are sitting around 65 per cent, down from about 79 per cent a year ago.

So far this year, water usage peaked on Saturday, January 12 when the overnight low was 21 degrees after a 38 degree day on Friday. Canberra and Queanbeyan used a combined 205.92 megalitres.

But Owen Gould, who is responsible for water planning and modelling at Icon Water, said it was only a modest yearly increase and the water supply for Canberra was "very secure".

"Across Canberra, we saw a dramatic 40 per cent decrease in water consumption per capita in response to the "millennium drought" and consumption has not returned to pre-drought levels since," he said.

"People are doing the right thing."

There have been no significant increases in the amount of stored water since October 2017, according to data published by the water provider.

The Corin Dam, which provides the cheapest water supply for Canberra, is currently 26.5 per cent full, while the Bendora Dam, which is the smallest catchment, is 77 per cent full and Cotter Dam is 95.1 per cent full.

Googong Dam is currently at 67 per cent capacity, meaning 181.37 gigalitres of water is available in the Canberra water supply.

In 2017-18, Canberra and Queanbeyan used 52.2 gigalitres of water.

"So there is still many years of supply available across all of these storages if these dry conditions continue into the future," Mr Gould said.

"We can survive a drought like the 'millennium drought' without water restrictions," he said. "We're confident we won't run out of water."

The "millennium drought" affected most of southern Australia and lasted from the 1990s until 2010.

In 2017-18, Canberrans used on average 312 litres a person per day, a 4.6 per cent increase on the previous year owing to hot and dry conditions and below average rainfall.

Mr Gould said a 50,000 year model that takes into account climate variability, population growth and changes in environmental water flows showed the water supply for Canberra was stable and secure.

"We expect that our source water system in its current state will meet the required level of service for many decades to come," he said.

Icon Water's manager of corporate affairs, Bronwen Butterfield, said it was always worth reminding Canberrans of the permanent water conservation measures in a city which has grown considerably since the "millennium drought".

"These measures are based on 'common sense usage' and allow flexibility, but promote sensible uses of water and prevent wastage. They include watering gardens using drip systems and in the cooler parts of the day, and discouraging the use of water to clean paved or concreted areas.

"We encourage residents to observe these measures and look for other opportunities to be water wise during the summer to save both water and money," she said.