Angry Melbourne consumers have confronted the city's water retailers about their soaring bills at a public forum.
Average household water bills will jump by nearly $300 next year, mostly to cover costs relating to the Wonthaggi desalination plant.
Retailers are reluctant to spread the rise over five years, because they say that would force them to borrow money to balance their books.
Yarra Valley Water's managing director Tony Kelly says the company decided it was best to increase charges in one big hit.
"The majority of customers said, 'look we want to get the pain out of the way'," he said.
"We looked at trying to smooth it over a longer period of time.
"The difficulty with that is we would have to borrow in the short term to cover the shortfall, and by the end of the five-year price period, the price is actually higher." Melbourne Water's managing director Shaun Cox says it would also have to borrow cover a shortfall.
"We did contemplate options of not matching the revenue and the costs, and that means that there's actually then a revenue shortfall that has to be paid for by way of borrowing additional funds," he said.
The retailers have promised more help to the thousands of customers who are already on hardship payment plans.
But customer Mario Pallotta says struggling householders should not have to deal with such a big jump in their bills.
"It's such a huge increase you'll find that if this had happened in other countries, especially like in Europe, especially like Greece, they'd probably riot over something like this," he said.
Tony Kelly says water retailers know low income families will be hit hard.
"The price rise next year of 33.7 per cent is a dramatic price rise, there is no doubt about that," he said.
"We are very conscious of the impact that will have on vulnerable customers in the community, we are putting in place a number of programs to try and ease the pain.
"We are going to develop a smooth pay product to enable customers to pay on a weekly, fortnightly, or monthly basis." The Essential Services Commission is assessing the water retailers' five-year plans.
It will make its final decision on water prices next June.