The Berejiklian government is yet to commit to a source of electricity to power the expansion of desalination in the state, potentially locking in a significant new source of greenhouse gas emissions for NSW.

Sydney's existing $2.3 billion desalination plant is 100 per cent powered by renewable energy as part of a 20-year deal signed in 2008.

Water Minister Melinda Pavey declined to commit to the preferred energy source to run the planned doubling of the plant and two other such facilities including in the Illawarra.

Sydney's desalination plant is currently powered by renewable energy. What happens to the expansion could have a significant impact on NSW's emissions and energy. Credit:Getty Images

"We are fast-tracking the next level of planning in concurrence with the trigger points in the metropolitan [water] plan," Ms Pavey told the Herald.