The planning of future sustainable water and wastewater system is not a trivial task. It involves all relevant aspects of sustainability such as defined by the Urban Water conceptual framework: health, environment (including use of resources), economy, socio-cultural aspects, and technical function. The Urban Water programme has developed a set of tools for the assessment of the aspects involved. Substance flow simulation models such as URWARE and SEWSYS deliver quantified data on emissions to air, water and land, and the use of energy. Data is interpreted by LCA methodologies, quantifying e.g. eutrophication, acidification, discharge of green-house gases etc.
All information, whether quantitative or qualitative, whether delivered by professionals or laymen, are used in an iterative decision-making process, such as the SCA method (Strategic Choice Approach). The multi-criteria assessment involves a weighting mode and can be made using graphic computer programs or numerically.
The SCA approach and the Urban Water tools have been used for assessing the future sustainable system for handling wastewater and biowaste in Göteborg, Sweden. Among the results were that it was not found to be sustainable to abandon the existing principles and exchange the existing system for source separation systems. Systems that extract pure phosphorus (and nitrogen) fractions at the treatment plant, and systems that aim at producing a very clean sludge by reducing the pollutant sources in the city, got high scores in the assessment.