Contamination: The unfolding scandal of toxic water in Australian communities.

“You've been giving your children water that's contaminated with chemicals…. so you're just trying to get your head around what does that mean?” Katherine resident

It’s one of the biggest environmental scandals in Australian history. Harmful chemicals, leaching into the ground and waterways, contaminating the water relied upon for drinking.

“They became more and more certain…It was also in the food chain, and it was also a risk to human health. Their own report by their own expert made that clear, that there was a risk to human health.” Investigator

These chemicals are the toxic legacy of fire-fighting foam, used for decades on Defence Force bases and other sites around Australia.

“They told us…this is the new asbestos. Those words exactly. That was them, giving a determination on how bad these foams were and that we had to pay attention to what they were telling us.” Oakey resident

Communities, living in the shadow of three key defence bases, have been trapped in a kind of no-man’s land for the past three years after it was revealed these chemicals, known as PFAS, had seeped out of the bases and contaminated the surrounding areas.

“The Department of Defence was careless in their use of this product on the base. They recklessly used it and they should've been taking more care.” Lawyer

On Monday, Four Corners investigates the gross failures by the Defence Department that led to this chemical contamination.

“I was horrified that this chemical was in such widespread use across Defence, and that we didn't have in place the appropriate measures to manage the potential risks, both to our people and to the environment.” Former Defence Manager

Reporter Linton Besser uncovers the troubling history of the use of these chemicals and reveals just how long the public was kept in the dark.

“They wanted to keep the matter under wraps, so to speak. They didn't want to go public on the issue.” Investigator

The impact on those affected is profound. Some rely on water supplies trucked in by Defence contractors. Others are trapped financially, unable to sell, with their homes officially designated as a contamination zone. All worry about the implications of exposure to these chemicals.

“It's petrifying as a parent. I don't think any parent in Australia would want to be told that, their youngest daughter, who's only four, has got those levels in their blood.” Oakey resident

Four Corners has discovered that the scale of the problem is continuing to grow as more and more sites around the nation are being tested for contamination.

“It's going to take a very long time to work through all of the issues that are associated with that. It could cost billions of dollars to try and solve this problem.” Former Defence Manager