 Drug use is a complex, hidden and often highly stigmatized behavior. This is also why measuring it is such a difficult task. Surveys, for example, are important tools, but as other tools, they are subject to biases. Some users are hard to reach and might not respond to surveys at all. Those that do respond might not admit the extent of their drug use. Others are unaware of the actual substances and the mix of drugs taken. To get a full picture of drug use, we need to use multiple indicators and dynamic monitoring tools. WasteWatt Analysis is a rapidly developing scientific discipline that has the potential to provide objective and real-time data on geographical and temporal trends in illicit drug use at population levels. How does it work? Most of the chemicals that enter our body leave it unchanged or as a mixture of metabolites. Drugs are no exception. Let's take a look at cocaine, for example. When cocaine is used, the body's metabolism breaks down its chemical compound. When this biochemical process is completed, the result is, among other compounds, benzoyl agonine, the main metabolite of cocaine. Benzoyl agonine ultimately ends up in the sewer network, most probably geographically close to where the cocaine has originally been used. The sewer network carries the wastewater to the treatment plant, where samples of the untreated liquid are collected. The samples are then taken to a laboratory, where the metabolites can be identified and their concentrations measured. Taking into account other factors such as sewage flow and population size, this information can then be used to back-calculate the amount of cocaine that would have been used by the population served by the treatment plant. Future research needs to address current limitations of the method. But combined and integrated with more established methods, wastewater analysis has the potential to give us a much clearer picture of drug use in Europe.