Abstract Environmental information is available to managers through a broad range of methods and tools, from raw data provision to knowledge-based decision support systems. The design of ‘environmental information systems’ (EISs) to enhance the use of environmental information includes consideration of data formats, user interface, the nature of management questions, data characteristics such as variability, reliability and periodicity, and the management culture within which the EIS is intended for use. One of the principles of EIS design is that the designer must know potential users — their wishes, needs, likes and dislikes. Interface prototyping is an approach to EIS design that provides designers with useful information about users and their interaction with the EIS under construction. A case study of interface prototyping in EIS design was carried out in development of a water balance assessment program for farm management planning. It was found that the approach opened the minds of potential users to the opportunities afforded by a well-designed information system, provided identification of required data, imposed a scientific rigour that transformed an ill-structured problem into a structured one, and resulted in widespread use of the program.