In vitro bioassays including cell-based bioassays and low-complexity whole-organism assays have been applied for decades in water quality monitoring. However, there is no common understanding what level or response is acceptable. As of now, bioassay results were only benchmarked against each other but not against an absolute measure of chemical water quality. The EU environmental quality standards (EQS) differentiate between poor and acceptable surface water concentrations for individual chemicals of concern but cannot capture the thousands of chemicals that are in water and their biological action as mixtures. We developed a method that reads across from existing EQS and makes additional mixture considerations to assure that the derived EBT are protective for complex mixtures as they occur in surface water. The EBT derivation method was applied to 48 in vitro bioassays with 37 of them having sufficient information to yield preliminary EBTs. 30 of those were considered robust enough to pursue further and for the remainder it is necessary to obtain more experimental data for single chemicals but also to derive more EQS values. To assess the practicability and robustness of the proposed approach, we tested the EBTs numerous case studies from the literature where wastewater treatment plants and surface water were evaluated with bioanalytical tools. In this presentation, we highlight specifically case studies from the EU project SOLUTIONS, where water quality was assessed in large streams (e.g., Danube), hot spots of contamination (e.g., disposal of untreated wastewater into the Danube in Novi Sad) and influence of wastewater treatment plant effluent into small creeks (case study of small Rhine tributaries in Switzerland). In many cases the proposed EBTs were able to differentiate wastewater from surface water and EBTs for different bioassays gave very consistent results indicating the benefit of a common derivation method. Despite the limitations due to limited effect data availability and limitations of the existing lists of EQS, the proposed generic methods to derive EBTs is a first step to harmonise existing approaches and explore various different options of a large diversity of in vitro bioassays commonly applied for water quality assessment. Acknowledgement – This study was a joint effort of the EU project SOLUTIONS (grant 603437) and the workgroup bioassays of the NORMAN network.