About 700g of methamphetamine has been found on a weekly basis in sewers in both Christchurch and Auckland.
Photo: 123RF
Authorities today released the last three months' findings (PDF, 381KB).
In Auckland, where one wastewater treatment plant was tested, more than 700g was found each week in December. In January it was 450g and in February it was almost 800g.
In Christchurch, the amount found in December was similar to the sample from Auckland. In January, about 650g was found and in February it was 730g.
Other drugs found in the two cities' sewers included cocaine and MDMA - with the latter more common in the sample from Christchurch.
The pilot programme, jointly led by Customs, the Ministry of Health and police, aimed to get an accurate picture of drug use in the cities.
Assistant Police Commissioner Bill Searle said there was not enough data to draw conclusions yet.
"But already what we can tell is that there's no heroin or alpha-PDP detected in either of the sample sites. So that's very positive for the communities living in those locations."
The pilot aimed to build a more accurate picture of drug use over a 12-month period, he said.
Today's release followed the results of separate research by Massey University and the University of Queensland, based on daily samples from two plants in Auckland over three months in 2014.
That study detected 600g of methamphetamine on average each day.
Some other drugs, like MDMA and the common ecstasy substitute methylone, were found in smaller amounts, but only at the weekends.