A new report shows doubling Australia's renewable energy could free up much-needed water supply for farmers.

The International Renewable Energy Agency reports water withdrawals in 2030 could drop by more than a quarter in Australia if there is a doubling of renewable energy capacity on 2010 levels.

The UN-backed organisation found solar PV and wind withdraw up to 200 times less water than conventional power generation including coal, natural gas and nuclear.

Victorian fruit grower John Pettigrew says coal and gas mining ventures are buying up water resources that could otherwise be used by farmers.

"If we're going to protect food growing, we need to ensure farmers have stable access to water," Mr Pettigrew said.

"Investing in renewables is a win-win for farmers as it can help minimise the effect climate change has on our crops and redirect water resources."

Dairy farmer Marian MacDonald says coal and gas generation have been sucking up water and causing problems for Gippsland farmers for decades.

"The Latrobe Aquifer is dropping 1.5m a year and it is coal and gas production that's taking the bulk of it," Mrs MacDonald says.

"To be told I can't irrigate from the water source that runs under my property is infuriating.

"Some farmers will run out of water for their cows if the aquifer runs dry. We can't afford that to happen."

IRENA also found doubling Australia's investment in renewable energy by 2030 will:

+ have substantial benefits for the country's economy, with conservative estimates suggesting the move would boost GDP by 1.7%

+ improve welfare through the creation of thousands of jobs as well as reducing greenhouse gas emissions and the health impact associated with air pollution.