Water to be recycled

Mundaring Weir.
Mundaring Weir.

Groundwater recycling will supply the city with more than seven billion litres of water each year and would add to desalination as another water supply option. More than 40 per cent of Perth’s water supply will now come from groundwater, with 31 per cent from surface dams and 23 per cent from desalination.

The recycled water is purified before being re-injected into natural aquifers, mixing with groundwater, and undergoing natural filtration for up to three decades before extraction.

Revelations that Water Corp drew more than 130 billion litres from the Gnangara Mound last summer, following 159 and 165 billion litres respectively in the previous two summers, raised speculation about the sustainability of the precious resource.

The Department of Water said the superficial aquifer in Gnangara Mound had dropped by an average 2m in each of the past 15 years.

Unprecedented low dam inflows due to lower rainfall saw demand from the Goldfields and Agricultural Water Supply Scheme, which services 100,000 people from Mundaring to Kalgoorlie, easily outstrip natural supply.

Mundaring Weir supply was supplemented by pumping water from various Perth sources, including deep aquifers on the Swan Coastal plain and the shallower Gnangara Mound.

Total dam storage for the Perth metropolitan region is at 26.9 per cent capacity, down from 30.2 per cent at the same stage last year.

Though Mundaring Weir is at a respectable 39.6 per cent capacity, most of the water has been pumped up the hill.

Perth has had one of its driest winters on record, with total rainfall of 436mm up until the end of July ” only slightly higher than the 336mm recorded in the same period of 2012 and well below the average of 546mm.