EVIDENCE LIBRARY
Why Do Wastewater and Drug-Checking Data Tell Different Stories?
Australian New Year monitoring found methamphetamine dominant in wastewater but uncommon among drug-checking submissions. The apparent conflict shows why surveillance methods must be interpreted by population, place, and behavior.
Wastewater analysis and community drug checking can monitor the same drug market yet produce very different rankings. That is not necessarily a contradiction. A 2026 Australian study shows that each method observes a different slice of exposure, geography, and behavior.
What did the researchers compare?
Usman and colleagues analyzed 24-hour composite wastewater samples from five sites in Queensland, New South Wales, and Victoria during the seven days surrounding the 2024–2025 New Year. Liquid chromatography–tandem mass spectrometry targeted alcohol markers, conventional illicit drugs, and 54 new psychoactive substances.
The investigators compared those population-level signals with drug-checking data collected at a fixed service in central Canberra during December and January across several New Year periods. Submitted samples were chemically examined for identity and, for major drugs, purity.
What appeared in wastewater?
Methamphetamine produced the highest estimated illicit-drug loads across the wastewater sites. Cocaine and MDMA increased during New Year, and MDMA/MDA differences between New Year and nearby days reached exploratory statistical significance. Ketamine was consistently detected at regional locations and rose approximately 2.8- to 3-fold on New Year days at two sites.
New psychoactive substances included bromazolam and 2′-fluoro-2-oxo-PCE. Some compounds appeared sporadically or at only particular sites, illustrating how an emerging-drug signal can be geographically narrow.
What did people bring to drug checking?
MDMA, cocaine, and ketamine dominated submissions. Across the studied New Year periods, new psychoactive substances accounted for roughly 15%–20% of submitted samples. N,N-dimethylpentylone and 2′-fluoro-2-oxo-PCE were among the recurring unexpected compounds.
The striking contrast was methamphetamine: it dominated wastewater estimates but was rarely submitted to the fixed drug-checking service. Conversely, some low-frequency substances detected in submitted samples were absent from wastewater.
Why are the results different?
Wastewater aggregates excreted residues from an entire catchment. It can capture regular, dependent, and private consumption among people who never use a checking service. Drug checking samples are self-selected. A fixed service may disproportionately reach people using pills or powders in episodic social settings and people who are uncertain about a product.
The methods also answer different questions:
- Wastewater: Which targeted residues entered this sewer catchment, and what population-normalized load is estimated?
- Drug checking: What is in the particular samples voluntarily submitted, and how pure are they?
- Neither alone: Exactly how many individuals used a drug, who they were, or whether a detected product caused a particular medical event.
What are the principal limitations?
Holiday travel can make census population estimates inaccurate for a wastewater catchment, affecting back-calculated consumption. The sampling window was short, daily samples may be autocorrelated, and comparisons were exploratory. The drug-checking site was in Canberra, geographically separate from the five wastewater locations. The two datasets therefore describe different places, populations, and contexts; the study could not establish direct relationships between them.
Wastewater back-calculation also depends on excretion factors, analyte stability, flow measurement, and whether a compound has other sources or transformation pathways. Drug checking depends on who chooses to attend and what they submit. A substance present below a method’s detection limit may be missed by either approach.
Why triangulation is still valuable
When independent systems converge, confidence in a market signal may increase. When they diverge, the discrepancy can reveal a blind spot. Wastewater may flag regional consumption not represented at urban drug-checking services, while submitted samples can identify a rare substitute before its population-level residue becomes measurable.
Bottom line
Methamphetamine’s dominance in wastewater and scarcity among drug-checking submissions are compatible observations because the methods sample different populations and behaviors. Surveillance improves when results are triangulated without pretending the datasets are interchangeable.
Scientific source
Usman M. et al. “Understanding Consumption of Illicit Drugs and New Psychoactive Substances in Australia by Triangulating Drug Checking and Wastewater-Based Epidemiology.” Drug Testing and Analysis (2026). DOI: 10.1002/dta.70120. PubMed PMID 42429112.