Socio-technical transitions in water scarcity contexts: Public acceptance of greywater reuse technologies in the Metropolitan Area of Barcelona

Greywater reuse systems are becoming more and more common in the new multi-storey buildings of the Metropolitan Area of Barcelona. A main driver of this trend has been the recent approval of ambitious local regulations aimed at saving water and using decentralised, alternative resources in a context of growing scarcity. Users must assume new responsibilities in water management and new capacities need to be developed at the very micro level to attain a successful implementation of these regulations. A survey of 120 greywater users and in-depth interviews with the main actors of the water sector was conducted in the town of Sant Cugat del Vallès, in the Metropolitan Area of Barcelona. The municipality's six years experience on greywater use provided an exceptional opportunity to assess community perceptions during the socio-technical transition process. Sant Cugat was the first municipality in Spain that enforced the installation of such systems in new buildings. Results show that the perception of health risks, operation regimes, perceived costs and environmental awareness are, in different degrees, significant determinants of public acceptance. The main institutional, technical, and economic challenges that need to be addressed during the ongoing socio-technical transition process are also explored. Improving the level of knowledge of these systems among users would reduce the risk of social refusal of the new technology. Public authorities and implementers need to stimulate social learning processes with specific actions and build trust among residents in the new governance network if decentralised and alternative water supply systems are to find a place in the everyday life of urban populations.