The city's water use peaked just shy of 2 billion litres on Saturday, or 42 per cent more than typical for a September day, Sydney Water said.

Month-to-date water consumption is running at an average of 1.71 billion litres, about a quarter more than the same time a year ago.

Sydney's water usage so far for September is also comparable to the peak during last December and January, summer months that included several heatwaves, Robert Ius, hydraulic operations manager at Sydney Water, said.

"This dramatic increase can be attributed to both a drier lead-in winter and the difference in rainfall levels in September between last year and this year," Mr Ius said.

So far this month, Sydney's gauges at Observatory Hill have picked up a mere 0.2 millimetres of rain, compared with a typical September tally of 68.4 millimetres. Rainfall in September last year was bang on average at 70 millimetres.

With only a couple of days left in the month, the current meagre rainfall places it as Sydney's driest September on record, beating the 2.1 millimetres recorded in 1881, the bureau said.

And it's not just September that has been dry, with the two previous months almost as parched.

The July-September tally so far is just 24.4 millimetres, or about one-tenth the usual rainfall. It's also the least on record for the period save for the 22.1 millimetres recorded at Observatory Hill in 1907, the bureau said.

The next chance of rain for Sydney may be a couple of millimetres' worth from showers that may arrive late on Wednesday or into Thursday, Kim Westcott, a meteorologist with Weatherzone, said.

Many formerly green spaces across the city are "pretty scratchy, hard and dried out", Ms Westcott said.

A spokesman for Penrith City Council said irrigation of parkland had increased about 20 per cent from usual levels. The increase would have been more if the area had not be soaked by particularly heavy rain in March.

Heat spike

Along with the lack of rain, the mercury has been hitting levels punishing for humans and plants alike, while elevating the bushfire risk as vegetation dries out.

Saturday was the hottest September day on record, with average maximums of 35.82 degrees, easily beating the previous high of 34.2 degrees set in 2003 by 1.62 degrees, according to the Bureau of Meteorology. (See bureau chart below of temperature anomalies.)

While sea breezes kept the city's top to 32.2 degrees, inland suburbs such as Penrith sweltered in temperatures five degrees warmer.

Statewide, many September heat records fell over the weekend. Coffs Harbour's maximum of 38.8 degrees on Sunday beat the previous mark by by 3.6 degrees, making that site one exceptionally hot spot.

Sydney's most unusual record from the weekend was possibly its 6am Sunday reading of 28.1 degrees. According to the bureau, that was the warmest such result for September in records going back to 1955.

The city hadn't been that warm at 6am since January 18. It also wasn't far shy of the warmest non-summer record for that time of 28.6 degrees reached on 5 April 1986, the bureau said

Heat reprieve - for now

Weatherzone's Ms Westcott said it's unlikely the remarkable heat will return in the next week or so.

There are also signs the pattern of dominant high-pressure systems that have kept rain-bearing cold fronts well south of Sydney is beginning to break up. Even so, that might not make bring much relief to Sydney's rainfall deficit for a while yet.

According to the bureau, the next eight days at least will bring little in the way of rain for Sydney. (See chart below.)

???Despite the long dry spell, heavy rains at different points during the past year has meant Sydney is not at risk of water restrictions at this stage, a Sydney Water spokesman said.

The city's dam levels, though have lost 0.7 per cent in the past week, or almost 16 billion litres, WaterNSW data shows.

Storage levels remain at 88.5 per cent full, compared with 96.2 per cent a year ago.

"There are currently no water restrictions statewide, and none are planned in the immediate or short-term as dam and reservoir levels remain strong," a WaterNSW spokesman said.

Jimmy Turner, director of horticulture across the Botanic Gardens, said "measures such as hand watering have been increased to maximise water conservation during hotter than usual days".

Some plants, such as clivias in the Royal Botanic Garden, were blooming in the early-season warmth. Paper daisies in the Domain and at Mount Annan at the Australian Botanic Garden were also thriving.

"The native plants do quite well in these conditions," Mr Turner said.

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