Despite the wettest November in 20 years, Manjimup’s water supply is down 10 per cent on last year, the Water Corporation has warned.

The shire’s dam levels overall were still at just 35 per cent late last week, 10 per cent lower than in 2011, Water Corp regional manager Scott Moorhead said.

“The recent rain is welcomed, however only a limited amount will reach the dams with dry catchments soaking it up, and empty waterways retaining large portions of it,” he said.

Weather Bureau spokesman John Relf said Manjimup received 88.6mm of rain in November, in contrast to an average 46.5mm.

A cold front dumped 25.8mm on Manjimup on November 28 and 29, making it the wettest November since 1992 and the sixth wettest on record.

Mr Relf said the bureau was predicting an unusually wet summer after a wetter than usual spring.

“Spring rainfall for Manjimup was 242mm, and the average is 231.7mm.

“But July was pretty bad, the worst on record with 42mm.”

With water supplies low, the Water Corp is offering a new rainwater tank rebate of up to $1000 for residents who install a new tank or plumb in a tank that holds 2000 litres or more.

The rebate is available until May 2013 to property owners using scheme water in Bridgetown and Manjimup shires.

Fifty tanks were made available through similar programs in the past, and Mr Moorhead said this number would be reassessed as the program progressed.

“Eligible residents are encouraged to lodge applications as soon as possible.”

Recent modelling indicated that in the Warren Blackwood district, a 2000-litre tank could reduce a household’s scheme water use by about 10 per cent, he said.

A 49km pipeline connecting Manjimup to the Bridgetown Regional Water Supply Scheme is expected to be ready by winter 2013.