Icon Water urges emergency services to keep fire retardant away from dams

It follows concerns that the pink chemical could pollute rivers and contaminate water.

Icon Water is working to minimise the risk to the water supply as the bushfires enter the city's rainfall catchment area. On Monday, fire breached containment lines around Corin Dam.

The supplier said it consults with the Emergency Services Agency which organises the drop of the pink retardant from aircraft.

It accepts that protecting people whose lives are in danger is paramount but wants the pink chemical kept away from the city's drinking water.

"Firefighting retardants are only being applied in catchment areas following consultation with Icon Water to minimise the potential impacts on water quality and where possible, a one kilometre exclusion zone has been requested," an Icon Water statement said.

Some of the world's top experts on water are warning about the wider risks to the ACT from the fires, both in the coming months and in the longer term.

Professor Quentin Grafton of the Australian National University said there was a question about the quality of Canberra's water after the bushfires of 2003 and that could be repeated this time.

"Going back to 2003, we can recall that we did have water quality issues and we've got a risk of that happening now," Professor Grafton said.

The fires in the ACT have been in the south of the territory and that's where much of the water supply comes from, he said.

Professor Stuart Kahn of the University of New South Wales warned of the risk of algae and fish-kills if waterways became choked with ash and partially burnt wood.

He said it was unlikely that polluted water would get through to consumers but the cost of treatment would probably rise because of the bushfires.

The experts' warnings come after the bushfire breached containment lines protecting the Corin Dam

"We're working closely with Icon Water about water supply issues," Joe Murphy, ACT Rural Fire Service chief officer said.

On the question of whether the pink fire retardants dropped from the air might pollute water supplies, he said: "We do keep water supply safe and we have an understanding about the use of retardants and gels and what actions that might mean as fire goes on."

Apart from the immediate issues arising from big bushfires near water supplies, the experts said that there was a longer term worry.

Because so much vegetation has been destroyed, the growth of new trees and grasses will be much greater than usual and that means the new growth will take water which otherwise would go into Icon Water's dams.

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"There is a real potential for reduced inflows into the dams, given the size of the fires in the south," Professor Grafton said.

"Chemical reactions triggered by fire can release nutrients, metals and other toxicants stored in vegetation and soil," according to a statement by the federal government's Water Quality Australia agency.

"Rainfall after a fire washes these contaminants into waterways and reservoirs, which can have substantial implications for agriculture, human safety and amenity."

Icon Water said that improvements were made after the 2003 bushfires to protect Canberra's water quality.

After those fires, Canberra's water became cloudy, with increases in iron and manganese.

The company juggles the source of supply between the three big dams supplying Canberra. It takes water according to where the water is clearest and most abundant.

It can take water from different levels within the dam, according to analyses of its suitability. There are then treatment plants between the dam and consumer.