Western Australia's Water Minister insists households and businesses are still heeding the water-wise message despite a sharp rise in use following Perth's hottest September on record.

Key points: Amid record dry temperatures, water usage on WA's largest water scheme is 4 per cent higher than expected

Amid record dry temperatures, water usage on WA's largest water scheme is 4 per cent higher than expected Water Minister Dave Kelly would not be drawn on whether plans for a costly new desalination plant would be brought forward

Water Minister Dave Kelly would not be drawn on whether plans for a costly new desalination plant would be brought forward He says in the meantime being water-wise is the key message for consumers and that despite the overall spike, per capita water use is trending down

It has prompted warnings from a former state water minister that the Government may need to bring forward construction of a desalination plant, at a cost of more than $1 billion dollars, putting significant upward pressure on household water bills.

Figures from the State-owned Water Corporation show customers connected to the main network have guzzled more than 60 billion litres of water since July — about 2.6 billion litres above the agency's target.

WA's Water Minister Dave Kelly says overall the water-wise message is getting through to people. ( ABC News: Jacob Kagi )

Overall usage on the Integrated Water Scheme Supply (IWSS), which supplies over 300 billion litres of water a year to Perth, the Wheatbelt, Goldfields and parts of the South West, is more than 4 per cent higher than expected.

Despite the consumption spike on the state's largest scheme, Water Minister Dave Kelly has downplayed suggestions household water use is out of control.

"These figures can sort of bounce up and down, you can't draw too many conclusions from one year," he said.

"The consistent trend in WA is that people are heeding the water wise message and … per capita water use is trending down, that's a good thing."

Water use on the Integrated Water Scheme Supply, which supplies Perth, the Wheatbelt, Goldfields and parts of the South West, is significantly higher than target levels. ( The Water Corporation )

Push for desalination plant amid ever-drying conditions

Perth has just recorded the driest September since the 1970s, with high temperatures and low rainfall expected to persist across southern Australia into the new year.

On WA's south coast, Denmark is currently subject to the toughest water restrictions in the state after the Government announced it would need to build a pipeline from the neighbouring city of Albany to ensure the holiday town does not run out of drinking supplies.

Unlike Denmark, Perth and the regional towns connected to the IWSS are not entirely dependent on rainfall.

Two seawater desalination plants, built between 2006 and 2012 in response to a drying climate, supply about half the scheme's drinking water followed by groundwater sources, dams and recycled water.

This year there has been 37 billion litres of streamflow into the cities dams, the lowest run-off level since 2015.

Stage five water restrictions are in place in Denmark, on the state's south coast, after their main dam received just 14 per cent of its average annual streamflow this year to date. ( ABC News: Tom Edwards )

While Mr Kelly has said a new major water source will be needed eventually, he will not be drawn on whether it will come from another costly $1-billion-plus desalination plant or further investment in recycling.

Nationals MP Terry Redman, who served as water minister under the former Barnett government, said that infrastructure spend could come sooner than Treasury and taxpayers had hoped if water consumption is not curbed.

"It certainly is concerning that in the bigger areas the Minister is taking a slightly more lax approach to the behaviours in the communities than perhaps he is in the regional centres," he said.

"Desalination plants are clearly the next line of investment even in the high rainfall areas of the south coast.

"The cheapest source of water [right now] is water that we can save."

The construction of a new desalination plant in Perth is expected to cost taxpayers upwards of $1 billion dollars. ( Supplied: Water Corporation )

Climate change and water woes

Western Australia's drying climate, which has seen rainfall run-off into Perth dams drop by 90 per cent over the past century, has spurred successive governments into action to diversify water sources and educate the public on saving water.

Climate change has been singled out in water saving adverts by the Water Corporation. ( Supplied: The Water Corporation )

Last year, the utility launched an advertising campaign featuring people dressed as quokkas, cockatoos and trees teaching humans how to conserve water in the face of climate change.

Mr Kelly said two issues are intrinsically linked.

"Climate change is the driver behind the water issues that we're having across the state but particularly in the south west, what we've constantly said is that we need a national Government that really takes this issue seriously and can drive the policy changes that can deal with that issue … that's not inconsistent with saying to communities and individuals that you need to be water wise," he said.

"You need to tackle climate change at every level — that starts by how long you stand in the shower, how much water you put on your lawn, how robust your on farm water supplies are and also what action our national government is or isn't taking.

"Simply saying to people that you can solve WA's water issues by taking shorter showers would miss the point."

Nationals MP Terry Redman says Water Minister Dave Kelly has become fixated on climate change, instead of addressing water-wise behaviour. ( ABC News: Andrew O'Connor )

Mr Redman said he was concerned politicking was diluting the water wise message for the end user.

"I'm a climate change believer and a climate change supporter [but] I think the Minister has got the message wrong if he wants to discourage water use," he said.

"I remember as minister we used to look at campaigns, we got professional input for those campaigns, and as a result we invested in trying to encourage the community to reduce consumption.

"[The Minister] has insisted on there being a message in and around climate change, rather than a message to help people reduce consumption … as a result it seems we're now seeing an increase in water consumption across Western Australia, not a decrease.

"That's a trend we can ill-afford.