REVEALED: Sydney’s largest dam was silently shut off from the water supply, fearing it had been dangerously contaminated by mud and ash after fires and heavy rainfall
- Floods have caused bushfire ash and debris to flow into Sydney’s water supply
- Ash, debris and sludge were seen floating on the surface of the Warragamba Dam this week
- Authorities have switched to a different dam for a few days, but have now been switched back
- Drinking water is treated by filtration before it reaches the household tap
- There are risks that bushfire ash can cause toxic cyanobacteria and clogging filters
The largest dam in Sydney was cut off from the water network on Monday, fearing it was too polluted after heavy rainfall disrupted mud and bushfire ash.
The move was only revealed today when the dam was reconnected because the water was considered safe.
After last weekend, 320,000 hectares of burnt bushland sediment, ash and debris saw float on the surface of the water near the sheet pile wall – which led to the use of water from Prospect Reservoir.
There were also fears that could have washed fire retardants in the river basin.
NSW Water Minister Melinda Pavey confirmed that the dam was closed. “We just wanted things to be arranged,” she said.
Drinking water in Sydney is again extracted from Warragamba Dam (photo) less than a week after authorities have closed the supply over the fear of contaminated water
“Ongoing monitoring results confirmed confidence in the quality of the water available at Warragamba,” said a Water NSW spokesperson (stock image)
The dam, which holds 80 percent of Sydney’s water, was reconnected on Saturday.
“Ongoing monitoring results confirmed the confidence in the quality of the water that is available at Warragamba,” said a spokesperson for Water NSW ABC.
An incident response team has been established and is working with Sydney Water and NSW Health on further monitoring and disaster plans.
“The quality of the raw water in Warragamba is improving, but more inflows can cause a further deterioration of the water quality at the sheet pile wall,” said David NS, head of NSW water.
Bushfire ash also contains nutrients such as nitrogen and phosphorus that can stimulate the growth of cyanobacteria, also called blue-green algae.
Some cyanobacteria can produce toxic chemicals that require careful filtration of the water before drinking.
Precautions are being taken, such as floating booms to collect ash and sludge.
Smaller water sources such as the Nepean and Tallowa dams were also replenished during the recent rains, but level two water restrictions still remain in effect in Sydney.
Authorities have also recalled that public water is treated between the dam and the domestic tap.
Recent forest fires in New South Wales have burned hundreds of thousands of hectares of forest
“It is important to note that this problem only concerns untreated water in dam storage at the start of the supply chain and does not affect the quality of treated water,” said a NSW Water spokesperson.
Water filtration systems collect suspended particles in the water, but an increase in these particles, such as after a forest fire, can cause the systems to struggle and clog filters.
Health authorities can issue a ‘boiling water alarm’ when it is possible that water can be contaminated with microorganisms.
In cases where water can be contaminated with chemicals, a ‘non-drinking alarm’ can be issued.
Most national health and water department websites can contain information about alerts, for example Sydney Water provides a daily reporting function for drinking water on their website.
There are currently no warnings for drinking water in Sydney.
Recent heavy rainfall in New South Wales has washed bushfire ash and debris in water sources