Science education should foster students' epistemological view on models and modelling consistent with formal epistemology in science and technology practices. This paper reports the application of a curriculum unit in the classroom using an authentic chemical practice, "Modelling drinking water treatment", as the context for learning. An authentic practice is defined as professionals working on an issue guided by common motives and purposes, according to a similar type of procedure and applying relevant knowledge. The epistemology on models and modelling in the practice was analysed and anchored in the curriculum unit. The knowledge involved was captured in a design principle "content modelling". A design principle provides heuristic guidelines to reach the intended pedagogic effects in the classroom. Throughout the field tests, research data were collected by means of classroom observations, interviews, audio-taped discussions, completed worksheets, and written questionnaires. Students were able to evaluate the advanced model features of goodness of fit and reliability, and, to a lesser extent, validity. However, reflection on the modelling approach applied can be improved. The findings were used to reconsider the current completion of the design principle "content modelling". This study contributes to the acquisition of a knowledge base concerning the use of authentic practices as contexts for learning in chemistry education as well as in science education in a broader sense. (Contains 2 tables and 5 figures.)