Dunedin, Queenstown and Invercargill residents will have their wastewater tested to help the police better understand drug consumption in New Zealand.
The pilot programme is run by the police and the Institute of Environmental Science and Research (ESR) and would capture about 80% of New Zealand's population.
Testing would be rolled out to 38 sites across the 12 police districts this month.
In the South, testing will be done for methamphetamine, cocaine, heroin, MDMA, Fentanyl and ephedrine/pseudoephedrine.
The Dunedin City Council, Queenstown Lakes District Council (QLDC) and the Invercargill City Council have all given permission for wastewater in their areas to be tested.
DCC 3 waters group manager Tom Dyer said the council did not have any privacy concerns about the programme.
Once disposed of wastewater became the property of the council, Mr Dyer said.
A QLDC spokesman said ESR would provide information about the whole water catchment and the council did not believe there was a privacy issue.
Police commissioner Mike Bush said the testing helped police better understand drug use in New Zealand.
Wastewater from Christchurch, Whangarei and Auckland (Rosedale) has been tested since 2016,
Methamphetamine was the most used illegal substance in Whangarei, ecstasy in Christchurch and cocaine in Auckland, the testing showed.
Expanding the programme to other areas helped build a better picture of the prevalence of illicit drug use, Mr Bush said.
Police Minister Stuart Nash said the programme provided a cost-effective and non-intrusive measure of illegal drug consumption.
