Waste water testing in prisons can help reveal the level and type of jail drug use, research shows.
PhD student Emma van Dyken collected sewage samples at an unnamed Australian prison for several months and tested the water for substances including cannabis and prescription drugs.
Ms van Dyken said her work at the University of Tasmania showed the baseline level of drug use among prisoners.
She said it was more reliable than mandatory drug testing because inmates did not know it was happening, so they could not time their drug use to avoid it.
"We found that basically drug use in the prison reflects that in the outer community," she said.
Researchers can tell whether drugs have been ingested or dumped down the toilet because metabolised drugs show up differently.
She said the aim was not to punish individuals but to show whether drug supply reduction strategies, like searches and the use of sniffer dogs to detect drugs, were working.
"At the moment there's no real information that shows the efficacy of those strategies so with some long term sampling we could tell the effectiveness of those two interventions," she said.
She said a confidentiality agreement prevented her saying exactly what she found.
The waste water testing was revealed at the Alcohol, Tobacco, and Other Drubs Research Symposium 2014 being hosted in Hobart.
Another development unveiled at the forum was a mobile phone app aimed at helping young people track their alcohol intake and its effect on their behaviour.
The app is aimed at 18 to 24 year olds, and gets them to type in their drinks, how they are feeling, and respond to questions about their hangovers the next day.