Sydney will face its harshest water restrictions in a decade, with the Berejiklian government to announce new limits on watering gardens, washing cars and filling pools on Thursday.

Level 2 water restrictions will come into force for the city, the Blue Mountains and the Illawarra regions from December 10 as poor rainfall shrinks dam levels to new lows.

Sydneysiders are facing water restrictions until at least 2024. Credit:Louise Kennerley

The dam level for the greater Sydney catchment — including a major reservoir in Warragamba — was near to 46.2 per cent on Wednesday. The Cataract Dam in the Upper Nepean was at 26.5 per cent.

Premier Gladys Berejiklian said a rapid decrease in dam levels had made the higher restrictions more urgent - they were due to come into force in February.