Effect-based methods (EBM) are increasingly used to assess disinfected water quality as they can detect the mixture effects of all bioactive chemicals, including disinfection by-products (DBPs). In this review, we discuss the application of EBM to extracts of disinfected water, with bioassays for cytotoxicity, genotoxicity and oxidative stress response being most responsive to DBPs. The contribution of known DBPs to the mixture effect can be predicted from single DBPs’ effects using established mixture models. Regulated DBPs typically have a minor contribution to the observed effect. Effect-based trigger values can be used to determine if the treated water quality is acceptable.