The total water storage across greater Sydney is at 45.9 per cent,with dams depleting at a faster rate than during the"millennium drought",which saw levels plummet to 33.8 per cent in February 2007.
The WaterNSW document projected another"hot,dry summer"could lead to"emergency 35 per cent levels"by May 2020.
Ms Pavey said the government was"investigating measures to support Sydney’s water supply",adding"all options are on the table".
"The NSW government is also looking into the expansion of the Sydney Desalination Plant,currently operating at 100 per cent and supplying 15 per cent or 250 million litres a day of Sydney’s needs,"she said.
The document,titled"Drought Supply Options Study"and obtained by theHerald,recommended a benchmark of 30 per cent capacity as “the floor on which to base planning,not 0 per cent or empty.”
“We won’t know when our depletion target[of 30 per cent] will be reached,but there may not be enough time to wait and see,''the document said.