SYDNEY has had more rain in the past eight days than it usually gets in all of November, but it has barely lifted dam levels and has not helped clear the blue-green algal bloom that has taken over the city's biggest dam.

The rain, which has fallen heavily in city streets and created the usual suburban stormwater problems, could also do more harm than good for firefighters.

The soaking has eased the fire danger for the next few weeks but if more rain does not fall and the weather turns hot, the bush will quickly dry out again, said a spokeswoman for the NSW Rural Fire Service. The rain could spur the kind of grass and scrub growth that makes perfect fuel for bushfires, she said.

As of late yesterday, Sydney's dams were 57.5 per cent full, slightly higher than the 57.1 per cent a week earlier. In the 24 hours to 9am yesterday only seven millimetres of rain had fallen at Warragamba, compared with nine millimetres over the city and as much as 35 millimetres at Kings Langley, in Sydney's north-west. Over the week, Warragamba received 65 millimetres of rain.

But the city as a whole has received a nice drenching, with 80.4 millimetres of rain so far this month, compared with a November average of 77 millimetres, according to the Bureau of Meteorology.

Rain falling in the catchment area is soaking into the thirsty soil rather than running into the dam, said a spokeswoman for the Sydney Catchment Authority.

"We really need follow-up rains … it might make a difference to dam levels if it kept raining through to mid-next week," she said.

Today's showers are predicted to ease tomorrow, with fine weather on Sunday.

The catchment authority, Sydney Water and NSW Health have been monitoring the blue-green algal bloom at Warragamba Dam since it was detected in late August. The authority said tests were being conducted on raw and treated water before it is supplied to households and businesses.

"This testing has not detected any issues with the treated water being supplied," it said.

The rainfall story remains one of a divided state.

Between 25 millimetres and 50 millimetres has fallen west of the Great Dividing Range compared with 50 millimetres to 100 millimetres on the coast.

Some townships in the Murray-Darling Basin west of Albury and around Walgett remain bone dry.

But there is one cloud with a silver lining. The bureau said there was a higher than normal probability for good rains in eastern Australia over the next few months.