Spokeswoman Clare Lugar said the 2.3 billion litres of run-off into our dams between May and July was the lowest since records began in 1911.
�We are often asked if the dams are full after a few days of rain and we remind people that in our drying climate our catchments must be completely soaked before they produce any decent runoff,� she said.
Overall, the dams which supply water to two million people in Perth are 27.7 per cent full, 3.6 per cent lower than in 2014.
Last month, Perth�s drinking water supplies were boosted by a $21.2 million upgrade to the Jandakot Groundwater Treatment Plant and a new bore.
Water Minister Mia Davies said the local plant could now treat up to 60 million litres of water a day, up from 40 million litres.
She said the extra capacity would cater for the water produced by the new bore, which draws the resource from 800m below the surface from the deep Yarragadee aquifer.