The ongoing drought conditions and the rapid decline in dam levels have triggered the need for level two water restrictions across the region, as well as Sydney and the Blue Mountains.

Premier Gladys Berejiklian is expected to announce on Thursday the new water-saving measures will start on December 10.

The Illawarra has been under level one water restrictions since May.

The Illawarra's main water supply, Avon Dam, has fallen to 44 per cent capacity, while Cordeaux Dam is at 38.5 per cent and Woronora Dam, which supplies water to parts of the Sutherland Shire, Helensburgh and the northern Illawarra, is at 37.4 per cent capacity.

Cataract Dam, above the escarpment from Wollongong, has fallen to 26.5 per cent and was taken offline for drinking water in September.

Level two water restrictions include all level one restrictions, and:

- Watering lawns and gardens to be watered by a bucket or watering can between certain times (to be announced). Unattended hoses and sprinklers are banned.

- Cars can be washed at home with a bucket and rinsed with a trigger hose on the lawn between certain times (to be announced). Cars can be taken to a commercial car wash.

- Swimming pools can only be topped up for 15 minutes per day using a hose with a trigger nozzle.