The results showed methamphetamine, codeine, morphine and methadone were detected with high frequency - showing up in between 80 to 100 per cent of days over the sampling period - followed by amphetamine, MDMA and methylone.
An overall mean of 360mg of methamphetamine and 60mg of MDMA, better known as ecstasy, was estimated to have been consumed per day per 1000 people.
While methamphetamine consumption was found at similar amounts in both catchments - at levels of 377 and 351mg per day, per 1000 people - cocaine was only detected in one catchment, and on only eight occasions.
Two of the detections identified cocaine but not its metabolite, suggesting the disposal of raw cocaine into the sewer rather than cocaine consumption.
Methamphetamine, codeine and other opioids were detected at a consistent level throughout weekdays, while ecstasy and methylone, a common ecstasy substitute, were detected only during the weekends.
Wilkins said this suggested they were used primarily as party drugs.
"The consistent use of amphetamine and methamphetamine suggests their use is not limited to late-night weekend partying," Wilkins said.
"The stimulant properties have long been known to be used across a range of work, domestic and recreational activities that require long periods of stamina and concentration."
Wilkins said it was not surprising that methamphetamine showed up more regularly, as it was also associated with high levels of dependency, which could also dictate more regular use patterns.
"I think methamphetamine use is a concern and this is confirming that this is a serious problem," he said.
"It wasn't unexpected but it's certainly verifying what we've been getting from self-reported data collection."
The low level of cocaine consumption was meanwhile consistent with the very low use and availability of the drug, as reported in annual monitoring surveys.
Cannabis was not among the drugs sampled as it tended to bind to solids and required extra testing which was proved expensive and outside the pilot study's budget.
Wilkins said the study was valuable as an "objective scientific verification" of drug use, avoiding the limitations of other approaches such as drug seizure data and self-reported surveys, but added that the study couldn't put a figure on how many people in Auckland were using each drug.
"You could try to estimate how many people had used that drug if you had an average consumption figure, but of course, that could mean a small amount of very heavy users or a whole lot of occasional users.
"In terms of prevalence, it's not something we'd use this research for."
Wilkins expected the data would be useful to police, but noted that testing for illegal drugs wasn't the only way the approach could be used.
"It's actually a really excellent way to gain data on a whole lot of health measures for a population: it could be used to include anything from diet to alcohol and tobacco use."
"But I think the real strength of this is it can be done in a whole lot of small towns and cities throughout New Zealand and for the first time, you can actually get some really accurate data about what's happening in those places."
While national data showed rates of methamphetamine dropping from 2.7 per cent in 2003 to 0.9 per cent in 2015, the methods to collect such data had limitations.
"Obviously, respondents data is dominated by people from the main centres - and you never get enough interviews to look at, what is the drug use in Hawera, for example."
The research was led by the Massey-based SHORE and Whariki Research Centre, along with environmental toxicologists from Queensland University's National Research Centre for Environmental Toxicology.
While wastewater analysis has been conducted in cities in Europe, North America, Asia and Australia, but this was the first time a study of this kind had been carried out in New Zealand.
The Massey study was separate from a similar project between police and ESR, taking place in Christchurch and Auckland's Rosedale treatment plants and targeting methamphetamine, cocaine, heroin, alpha PVP, MDMA and Creatinine.
A police spokesperson said it was too soon to draw comparisons between the Massey study results and those of the other, which were being finalised and due to be released soon.
