SHE'S made the headlines for her unforgiving "say yes" to a Labor carbon tax campaign and she's back again, this time as a water warrior.

Actor Cate Blanchett has unveiled her latest environmental project, a rainwater harvesting system installed in the Walsh Bay arts precinct in Sydney equivalent to half the playing field of the Sydney Football Stadium.

The harvesting, storage and reticulation system will capture rain from the expansive roof of The Wharf in Walsh Bay, which houses the Sydney Theatre Company (STC) and other arts organisations.

It will then be stored in a huge pipe that runs 500 metres under the pier, providing 100 per cent of non-potable water for all resident organisations.

It's one of only a few in the world and expected to save 11.3 million litres of water a year.

"Today is a great example of how many helicopters there are in the city of Sydney," Blanchett said as she was drowned out by blackhawk helicopters swooping around the harbour as part of an Australian Army training exercise.

"But it is a great example of how science and the arts are intimately connected. Both sectors are purveyors of experimentation and the embodiment of the imagination.

"We're all pleased to bring this innovative engineering technology into our creative lives today and indeed to be a showcase of how such systems can function to great economic and societal benefit.

"So, have a shower or use the loos."

The system, designed by Australian projects firm Sinclair Knight Merz (SKM), is the first of its size in Australia and is one of only a few in the world.

It is part of STC's Greening The Wharf project, which saw the installation of more than 1900 solar panels on the roof of The Wharf in 2010.

Organisations at The Wharf that will benefit from the system include the Bangarra Dance Theatre, Sydney Dance Company, Australian Theatre for Young People, Sydney Philharmonia Choirs and Regional Arts NSW.

"The entire project has been made possible through a unique collaboration with private philanthropists, corporate and government support, both state and federal, who really understand the incredible opportunity that greening this amazing arts precinct represents not only for the organisations down here but for the city of Sydney and the state," Blanchett said.

With Maryann Wright of news.com.au

Originally published as 'Use the loos' Blanchett opens new system