ASTA — A method for multi-criteria evaluation of water supply technologies to Assess the most SusTainable Alternative for Copenhagen

•Develop a method for combining sustainability dimensions in to one joint decision support system•Emphasize the relevance of assessing various criteria when choosing your water supply source•Develop and test a decision support system combining two multi-criteria assessments•Demonstrate that freshwater is a limited resource•Show water systems based on rain-& stormwater or groundwater are preferable in our case Graphical abstract of paper where sustainability is defined as the 3 dimensions – environment, economy and society. Environmental evaluation is built on LCA also covering the impacts of freshwater withdrawals which are presented by a recycling diagram around the globe where water scarce areas are highlighted in red. Economy is indicated by a Euro-coin and society by a person. [Display omitted] Utilities in larger cities have to make complex decisions planning future investments in urban water infrastructure. Changes are driven by physical water stress or political targets for environmental water flows e.g. through the implementation of the European water framework directive. To include these environmental, economic and social sustainability dimensions we introduce a novel multi-criteria assessment method for evaluation of water supply technologies. The method is presented and demonstrated for four alternatives for water supply based on groundwater, rain- & stormwater or seawater developed for augmenting Copenhagen's current groundwater based water supply. To identify the most sustainable technology, we applied rank order distribution weights to a multi-criteria decision analysis to combine the impact assessments of environment, economy and society. The three dimensions were assessed using 1) life-cycle assessment, 2) cost calculations taking operation and maintenance into account and 3) the multi-criteria decision analysis method Analytical hierarchy process. Specialists conducted the life-cycle assessment and cost calculations and the multi-criteria decision analyses were based on a stakeholder workshop gathering stakeholders relevant for the specific case. The workshop reached consensus on three sets of ranked criteria. Each set represented stakeholder perspectives with first priority given to one of the three sustainability dimensions or categories. The workshop reached consensus and when the highest weight was assigned to the environmental dimension of sustainability then the alternative of ‘Rain- & stormwater harvesting’ was the most sustainable