*News from the Sydney morning herald

Victoria has flicked the switch on a controversial north-south pipeline but there is no indication yet when Melbourne's water restrictions will be eased.

There is also uncertainty over the longevity of the pipe, which was hurriedly built as a stopgap to ensure Melbourne doesn't run out of water before a desalination plant opens at the end of next year.

Premier John Brumby switched on the pipeline amid tight security at Sugarloaf Reservoir, northeast of Melbourne, on Wednesday.

He described the $750 million project as the biggest boost to Melbourne's water supply in 25 years.

The 70km pipeline will pump 75 billion litres of water annually from the Goulburn River in the state's northeast to Melbourne through so-called "water savings" from irrigation upgrades.

However, some water in the first year will come from water quality reserves in Lake Eildon.

Mr Brumby said the pipeline was part of a "roadmap back from water restrictions", but would not be drawn on when stage 3a bans would be rolled back.

"We'll review our water supply situation as we go through the year," he said.

Doubts have been raised over the need for the pipeline amid revelations Melbourne's dams have enough water to see out the next two years, before desalination starts in December 2011.

In the event the water is not needed, it will be stored in Lake Eildon and on-sold or released into rivers.

Mr Brumby could not explain the pipe's future beyond 2011 but said it would take a long time for dams to replenish.

"I don't believe the pipe will ever be redundant," he said.

The pipeline will operate around the clock during the eight month irrigation season between August and May, pumping an average 300 megalitres of water into Sugarloaf Reservoir a day.

Melbourne Water project director Rod Clifford said the pipe could be reversed in future but that would involve a $100 million refit.

"If it's ever required, and I believe the government thinks it's unlikely ... it would need another significant pump station to be built down here at Sugarloaf (Reservoir) and that would then allow a reverse flow to be contemplated."

Branding the pipeline a white elephant, the opposition said it would not be needed if the government harvested the hundreds of billions of litres of storm and wastewater that flows into the sea each year.

Plug the Pipe protest group spokeswoman Jan Beer said the pipeline would enable Melburnians to water their gardens and wash their cars while northern Victorians were doing it tough.

And any surplus water would be sold to the highest bidder.

"I just find it really obscene, it's just inequitable," she said.