A fall in PFAS limits will have dramatic implications for Katherine where drinking water is already being treated and water restrictions are in place.

The lowering of limits, which is already happening across many states of the US, will not only impact on our drinking water but recreational water use as well.

It was a drop in PFAS limits in August 2017 which saw the NT Government immediately impose water restrictions in Katherine

"Nowhere around the world are they (limits) going up, or ever likely to," environmental scientist Peter Murphy said.

Mr Murphy was speaking to the Katherine Times from Canada where is studying the latest moves in PFAS science, both there and the US.

The Department of Defence has paid for a new waste water treatment plant at Oakey's Army Aviation Centre to take the PFAS contamination from groundwater using Mr Murphy's OPEC Systems treatment methods.

Up until now, Defence has been using the ECT2 plants sourced from the US.

"I also suspect the scope of what is considered to be PFAS to go wider as well," Mr Murphy says.

He said PFAS limits were "a dog's breakfast" with an incredible amount of scientific research into the subject going on around the world.

"We need to be careful how far we come down because we might create an unsolvable problem.

"Some US states are already pushing to go down but really we should wait for the science to come in first."

California and New Jersey, for example, have set their maximum limits for water at 13 ppt for PFOS and 14 ppt for PFOA.

There is one ECT2 plant removing PFAS from a megalitre of contaminated bore water a day from Katherine's drinking water.

Katherine remains on water restrictions until the promised bigger plant, capable of treating all the town's drinking water, arrives as expected at the end of this year.

Defence already has one ECT2 plant cleaning contaminated groundwater at the Tindal RAAF Base with a second expected to operational by the end of the year.

Until the Oakey development, Defence favoured the ECT2 technology which uses a synthetic resin which the PFAS sticks to.

While the method has been proven to work well, there is the problem of disposing of the PFAS saturated resin.

The new Oakey plant is designed by privately owned OPEC Systems which uses Surface Active Foam Fractionation technology to process up to 250,000 litres of PFAS contaminated groundwater per day.

Simply, the method involves bubbling the contaminated water into a foam.

"You vacuum the foam off ... it comes off like fairy floss," OPEC managing director, Mr Murphy said.

What mostly began as firefighting foam returns to PFAS-thick foam again, he says.

The method concentrates the PFAS into a toxic soup and a final touch up on the cleaned water using resin brings it down below drinking water guidelines.

Mr Murphy hopes by trialing the method at Oakey he can show the system is cheaper and more efficient than other methods.

"... our goal was not just to strip PFAS but to apply the principles of green chemistry which would allow us to deliver minimal waste and zero harm to the environment," he said.

"The strength of our approach is we have engineered a mechanical way to do this that is fast, efficient, sustainable and cost effective, with the capacity to continuously treat large water volumes. We believe this combination will be a game changer for PFAS remediation.

The waste water treatment plant will operate for a 30-month trial period.

Mr Murphy said many methods, including his own, were already successful working to remove PFAS from water.

"The big concern is the treatment of the contaminated soil."