The toilet and shower wastewater flowing from Christchurch and some Auckland homes will now enable police to monitor the amount of drugs consumed by residents.
In a New Zealand Government first, police said they will this week begin analysing wastewater in Christchurch as well as Auckland's Rosedale treatment plant.
Scientists will test for methamphetamine, cocaine, heroin, alpha PVP, MDMA and creatinine, which is used as the control.
Assistant Commissioner Bill Searle said the results will help authorities design better treatment and enforcement strategies and allow comparison with international testing results.
"Perth has done wastewater analysis testing, and announced earlier this year that 31.6kg of methamphetamine was consumed in the city area per week. That's 1.6 tonnes a year," he said.
"Perth can also measure things like peak days for use and the effects big seizures have on their usage rates."
Mr Searle said the testing for illegal drugs was not traceable to individuals and will not result in criminal charges against residents.
The Institute of Environmental Science and Research will undertake the testing, with samples to be taken in Auckland and Christchurch for seven days each month for a year.