Drugs tested for will include methamphetamine, cocaine, heroin, MDMA and fentanyl (file photo).

Wastewater testing will be rolled out across 12 police districts this month to better understand the population's drug consumption.

Police commissioner Mike Bush said expanding the programme to regional New Zealand and other large centres will help to create a better picture of the prevalence of illicit drugs in communities.

The programme is a joint venture by police and the Institute of Environmental Science and Research (ESR).

ESR has been conducting wastewater testing in Rosedale, Auckland, Christchurch and Whangarei for the past two years.

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Methamphetamine, cocaine, heroin, MDMA and fentanyl are currently tested for.

JARRED WILLIAMSON/STUFF Police commissioner Mike Bush said the programme would help get a better picture of the prevalence of illicit drugs in communities.

Previous results have showed a rise in cocaine detected in Auckland, from 36 grams per week in June 2017, to 95 grams in November 2017.

Cannabis testing will be introduced in Northland and Auckland and testing ephedrine/pseudoephedrine will be introduced at all sites as part of the programme rollout.

Bush said samples from the areas that are already tested have shown "extensive and diverse" patterns of drug use.

It had "significantly enhanced" the understanding around the demand and supply of illicit drugs and the impact it has on individual communities.

"Over the past 18 months, 1.5kg of methamphetamine was estimated to have been consumed on average each week across the three test sites. This translates to an estimated $2 million a week in social harm," Bush said.

"Expanding the number of sample locations will help us identify differences in drug use between geographic regions and will act as an early warning system for emerging risks."

Chief executive of ESR Keith McLea said the organisation had "extensive expertise" in testing wastewater.

"The pilot project provided real-time information about drug use patterns in the wider population which is proving invaluable in keeping communities safe," McLea said.

"We highly value our partnership with police and look forward to the national roll out."

Results from the new testing sites will help inform prevention and treatment strategies, allow comparison with international data and measure the effectiveness of education and enforcement, police said.

The four Auckland sites began testing on October 1. The rest of the site's will begin testing by the end of October.