Wastewater in the Netherlands has been examined for more than 20 years for traces of pathogens and other substances, such as genetic particles of poliovirus, antibiotic-resistant bacteria and drug residues. Since 2020, wastewater testing has also been successfully used to monitor the spread of the coronavirus SARS-CoV-2. Thanks to the success and increased popularity of wastewater testing, both the frequency and number of sites where wastewater testing is carried out has increased. RIVM is also planning to expand wastewater testing to include research on stress, lifestyle and non-communicable diseases, such as diabetes and certain types of cancer. The techniques used in this regard are also under development. Wastewater researchers defend the position that their measurements are not traceable to individuals and that the privacy of these individuals is not affected. However, with the expansion of the scope, scale, frequency and techniques used in wastewater research, the irreducibility of individuals in wastewater research is no longer a given. This academic essay describes both the possibilities of wastewater research as well as when the European General Data Protection Regulation (GDPR) is applicable and provides parameters to estimate the identifiability - and thus the applicability of the GDPR - of individuals through wastewater research.