Despite profound transformations of spatial development patterns, the "modern infrastructure ideal" of universal and standardized supply with infrastructure services continues to play an important role in discussions on the future of rural infrastructures in shrinking regions of East Germany. Regional planners have reacted to current demographic, socio-economic and environmental transformations by scrutinizing infrastructure standards, but have only begun to reflect upon enhancing the flexibility of infrastructure systems themselves. Until recently, infrastructure planning was treated as a more or less technical and economic problem, without taking into proper account regional specificities and local non-expert knowledge. This paper suggests that flexible, regionally specific and participatory approaches may offer opportunities for innovative and sustainable planning solutions also applicable beyond the infrastructure sector. Referring to the difficult case of the transformation of water supply and waste water disposal systems of Brandenburg in north-eastern Germany, the paper discusses (1) the mismatch between established infrastructure-related planning rationales and current planning problems and (2) potential guidelines that may be constitutive for sustainable water infrastructure planning in the future. These guidelines lead to more general reflections on how infrastructure planning may be conceptualized in view of transforming demographic, environmental and socio-economic conditions.