Comparison of methods for calculation of sustainability indices for alternative sewerage systems—Theoretical and practical considerations

City planners need practical methods to assess and compare the sustainability of different alternatives for urban infrastructure. This article presents the consequences of selecting different methods to normalize the values of sustainability indicators, and the influence of selecting different indicators and different weighting techniques. Chosen indicators represent use of resources, environment, health and safety, psycho/sociological situation. Infrastructure costs are not included in the indicators, since it is more convenient to weigh them against the sustainability indices of the different systems. All indicators are aggregated into one system index. A nature-based sewerage system is compared to a conventional system. The article demonstrates that the method used to normalize the indicators, the choice of relevant indicators and the weighting technique have considerable influence on which system is found to be the more sustainable.