Ecological aspects have gained increasing attention during recent decades in urban land use planning and site development. However, relatively little attention has been paid so far to mass and energy flows of urban infrastructure and utility systems in particular, in spite of their significant contribution to the total mass. In the first part of this paper, the mass of water mains and sewers is quantified in relation to the mass of buildings. The second part of the paper deals with the development of the stock of water mains and sewers from the past to the future. Future rehabilitation needs in terms of annual mileage of pipelines reaching the end of their service life are forecast with a cohort survival model. In the third part of the paper, some preliminary results are presented on the mass and energy flows of water mains and sewers. Conventional life cycle assessment methodology is applied to pipelines of different materials.

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