It's time to conserve water as dam's fall to lowest level in 10 years
South-east Queensland's largest dam has fallen to its lowest level in more than a decade, prompting a call for residents to reduce their water consumption.
Dams that supply south-east Queensland's drinking water are around half full
If they remain low, one option is to start using recycled water for drinking supplies
On Tuesday, Wivenhoe Dam, west of Brisbane, was at 36.2 per cent capacity, the lowest level since 2009, according to Mike Foster, from water authority Seqwater.
"That's the result of a couple of back-to-back effectively failed wet seasons where we saw some good rainfall in our coastal dams, but Somerset, Wivenhoe and North Pine Dam — our big central dams — unfortunately that rainfall has missed those storages," Mr Foster said.
He said inflows to Wivenhoe Dam were critical to keep drinking water flowing to the state's most populous region.
"Wivenhoe is by far our biggest drinking water storage, so Wivenhoe alone can account for almost 40-50 per cent of our overall drinking water storage," Mr Foster said.
The combined level of all south-east Queensland dams is sitting at 56.4 per cent.
Based on the current rate of usage, the region's dams could hit 50 per cent capacity by September.
If that happens, water restrictions would be considered, including limits on outside cleaning, watering gardens and topping up swimming pools.
"Given where our dam levels are, we're absolutely encouraging the community to look at ways they can conserve and reduce their water use."
Right now, each person in south-east Queensland is using 170-175 litres each day — around 20-25 litres more than dam managers would like.
Some smaller Scenic Rim communities are already having to limit their water usage.
Water grid put to the test
Mr Foster said the construction of the south-east Queensland water grid had given authorities "more weapons in our arsenal" since the Millennium Drought, which ran from about 2001 to 2009.
The south-east Queensland water grid is a network of pipelines connecting the region's dams, water treatment plants, a desalination plant and reservoirs.
It enables water managers to move drinking supplies around the system.
"We've got the water grid, we've got the Gold Coast desalination plant and we've certainly got the Western Corridor Recycled Water scheme and combined, that certainly puts us in a better position than we've ever been to manage through drought," Mr Foster said.
"The way we're operating the water grid at the moment, we're effectively moving as much water as we can from the Gold Coast and as much from the Sunshine Coast to really try and preserve those big central dams, in particular Wivenhoe," he said.
If dam levels continue to dwindle, purified wastewater could be used to top up drinking supplies for the first time, through the Western Corridor Recycled Water Scheme.
But Mr Foster said that move would need state government approval and it could take years for the recycling plants to start operating.
"The Western Corridor is made up of three purified recycled plants, to get all three of them all up and running it'd take us a couple of years.
"There's a really strict verification, validation process, we need to work really closely with Queensland Health and the water supply regulator," he said.
Recycled water is currently being used to supply the Tarong and Swanbank power stations.
Hopes pinned on autumn rain
The Bureau of Meteorology said summer rain had been below average in parts of south-east Queensland, including the Wivenhoe Dam catchment, even though there was a La Nina system in place.
"It is quite a weak La Nina and we haven't seen that same widespread, above average rain fall, as we saw during the 2010 to 2011 La Nina," said climatologist Felicity Gamble.
But Ms Gamble said there are "optimistic" signs for more rain from March to May.
"Overall, for autumn, we are seeing increased chances, so around 70 per cent chance, of getting above median autumn rainfall," Ms Gamble said.