Sewage data helped motivate the Turnbull government to crack down on welfare-fuelled drug abuse, it has been revealed.
The data, from a National Wastewater Drug Monitoring Program assessment, identified "astonishingly high" rates of methamphetamine use across Australia.
The figures prompted the government to act, Social Services Minister Christian Porter said.
"We want to drive behavioural changes to some of those areas at that critical point where people are job searching," he told reporters in Canberra on Thursday.
The controversial drug testing trial, announced in Tuesday's federal budget, will apply only to new welfare entrants and consider compliance track records.
Treasurer Scott Morrison earlier confirmed sewage will be tested to find areas of high drug use, which will then be selected as trial sites for testing new welfare recipients.
Under the plan, those who fail more than once will be referred to medical professionals for assessment and treatment.
Welfare lobby groups have argued that the approach will treat recipients like criminals.
But Mr Porter said the measures were designed to identify those struggling and help them get their lives back together.
"As a government, we want to work with those people to ensure that if they do have barriers, they are addressed," he said.
"We are doing something very important and it is surprising this hasn't happened before."
Human Services Minister Alan Tudge said welfare was for the basics and should not be abused.
"It is not there to support a drug, a gambling or an alcohol habit."
