Next year, Victoria’s desalination plant will be turned on for the first time.

The multi-billion-dollar plant has sat idle since it was completed in 2012, but the state’s water storages are now so low that it will have a job to do soon.

With Melbourne's water storage now at 63.8 per cent, down from 72.1 per cent this time last year, the State Government ordered 50 gigalitres of desalinated water to be delivered next summer.

The Government said inflows to local catchments were at 306 gigalitres in 2015, even worse than the average at the height of Victoria's millennium drought of about 376.

The running of the plant “will see an impact of $12 a year on each household”, according to Water Minister Lisa Neville.

“This is about making sure that we can continue to provide certainly to business, continue to grow jobs, and also ensure that our kids can play on sporting ovals that aren't cracked,” she said.

“We're hoping that this decision ... provides the buffer we know we need and we're all hoping for [for] everyone in Victoria who is doing it tough in relation to the lack of water and rainfall.”

The Victorian Chamber of Commerce welcomed the move, but Opposition water spokesperson Peter Walsh said it was a unnecessary move to make the Government look like it was doing something.

“Melbourne's water storages are two-thirds full and we're not even on water restrictions, but Daniel Andrews has rushed off and ordered 50 billion litres of expensive desal water,” he said in a statement.

“Today Daniel Andrews has shown he doesn't care that he's forcing up water bills and making life harder for Melbourne families.”

Melbourne dealt with heavy water restrictions for several years, but now has permanent water use rules in place.

Outside the capital, the regional towns of Korumburra, Poowong, Fish Creek and Loch are on staged water restrictions.

The Government has also launched the Target 155 campaign, encouraging households to limit their water use to 155 litres a day.

“A target about promoting conservation amongst Melburnians, we know that Melburnians have really changed their behaviour in terms of water use, but we want to continue to encourage people to see water as very, very precious,” Ms Neville said.