Data from Australia’s wastewater drug monitoring program suggests methamphetamine use (also known as speed, ice or crystal meth) is at a record high. Cocaine is also up. MDMA may be levelling off. Heroin is fluctuating.

At first glance, these findings from the Australian Criminal Intelligence Commission this week sound alarming.

But before we draw big conclusions about worsening drug use, it’s worth taking a closer look at what this data can and can’t tell us.

What wastewater data actually measures

Wastewater testing works by analysing sewage for traces of drugs people have used. Researchers test samples from treatment plants to estimate how much of a drug has been consumed by the population connected to that system.

It measures metabolised drugs. So it’s able to tell the difference between drugs that have been flushed down the toilet and drugs that have been excreted.

It’s a clever method that avoids some of the issues of self-report surveys, where people may under-report illegal behaviour.

It also gives close to real-time data unlike population surveys that are only conducted every few years.

But wastewater data can only measure the volume of drugs consumed, not the number of people using them or level of harm they experience.

Wastewater data can’t differentiate quantity from frequency. When it shows increases in particular drugs, we don’t know whether there are more people using the drug, or if the same people are using more of the drug, or using it more often.

It also can’t identify........

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