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Illicit drugs detected in New Zealand's wastewater in the last few months would have generated almost $500 million of criminal profit over a year.
And on average Kiwis use $8.9 million worth of drugs each week.
Police have released the results of the national wastewater testing programme for the third quarter of 2019, which reveal more insight into the drug habits of New Zealanders.
Described by scientists as "one large urine test", the wastewater testing started with three sites in 2016 - Whangarei, Auckland's North Shore and Christchurch - but was rolled out nationwide last November.
The ESR testing at 38 sites now captures 80 per cent of the population.
Drugs tested for include methamphetamine, cocaine, heroin, MDMA and fentanyl.
Police say the key finding of testing between May and July is that the average weekly use of detected drugs had an estimated street value of $8.9 million.
This is estimated to generate approximately $464 million of criminal profit annually.
Methamphetamine remains the most commonly detected illicit drug nationwide, with approximately 15kg consumed on average each week.
Detected average methamphetamine use translates to an estimated $19 million per week in social harm.
Annually, this could equate to more than $1 billion.
Police said methamphetamine use was most prevalent per capita in the Northland area
followed by Hawkes Bay.
The second most commonly detected illicit drug across New Zealand was MDMA - with an estimated consumption rate of 7.9kg on average each week.
MDMA use was most prevalent in Southland and across the Auckland area.
Police said cocaine was detected in low quantities - approximately 907g on average each week.
"This indicates a much smaller user base and likely reflects less demand and supply associated with the drug," they said in their third-quarter report.
"Cocaine use is significantly more prevalent in the Auckland region (per capita) than anywhere else in the country."
Fentanyl was also found - but in low quantities, around 1g a week nationally.
The majority was located in Northland but police said that result had to be viewed with caution as the detected average usage across all testing sites is extremely low.
"The aim of testing for fentanyl is to establish a baseline of consumption so, over time, [police and the Ministry of Health] can determine any fluctuations in the consumption," police said.
"A baseline for consumption remains unclear at present.
"As fentanyl has only been tested for very recently, it is too early to draw conclusions about what proportion of the fentanyl in wastewater is illicit."
Heroin was not detected at any of the testing sites between November 2018 and July 2019.
"This is consistent with other indicators that the opiate user population in New Zealand is very low," police explained.