Restricting Melbourne's urban sprawl could have a big impact on reducing the city's water use over the long term, says a CSIRO report launched to coincide with National Water Week. The report aims to inform and promote discussion about the links between urban water and energy policy to identify the best overall options to secure Melbourne's future water and energy needs.

"The relationship between water and energy policy and management is a complex one and is often ignored," says CSIRO project leader Mr Steven Kenway from the CSIRO Water for a Healthy Country Flagship.

"Our research shows that water use may increase by 50 per cent if urban sprawl and energy use continues at the same pace."

Scientists have analysed the implications of increased energy use, as well as the effect of other big drivers such as urban form and population, on Melbourne's water supply.

"A compact urban form over a sprawling Melbourne could potentially save 100GL of water by 2045," Mr Kenway says.

"Savings would mostly come from reduction in outdoor water use.

"Substantial energy savings can also be won at the consumer level. The widespread adoption of solar hot water systems plus reduced water demand could more than offset anticipated energy increases that are associated with future water provision ways such as desalination. This is because around 10 times more energy is used to heat residential water compared to the energy used to provide water to households."

Reducing overall energy consumption would be another way to save water, he says.

"Generating electricity requires water and it is estimated that this demand will almost double over the next three decades to around 225GL per year unless different energy options or technologies are introduced," he says.

He says further research is needed to better characterise and understand the energy and greenhouse