The increasing use of digital technology has many advantages, but is insufficiently used in urban water management. This article describes a workflow based on detailed German rules and regulations for the use of routine data from wastewater treatment plants (WWTP) for design, assessment, benchmarking, and activated sludge modelling. Our workflows use data that are routinely collected. However, prior to use the data must first be checked. It includes data import, plausibility checks, data evaluation, and subsequent plant design. In addition, the data available in the system can be used to supply an activated sludge model of the plant as a basis for use in redesign and process optimisation. The main advantages of such an approach are time savings, increased quality, and a transparent and comprehensible procedure. Exemplary results are presented for individual elements of the workflow. We also provide a comprehensive classification of the question in the context of environmental data science. WWTP routine data bases are an important source for information needed for evaluation and optimisation.