Human societies and ecosystems use water in different ways and at different scales, which complicates the study of water-use sustainability in socioecological systems. We present a multiscale integrated assessment of societal and ecosystem metabolism, an innovative approach to the quantitative analysis of water use that addresses the problem of multiple scales. It builds on the concept of metabolic pattern and the flow-fund model of Georgescu-Roegen. We show how to define water resources and water use (expressed in hourly rates) for socioeconomic systems in relation to the identities of relevant fund elements (relevant categories of human activity or land use) over a time span of 1 year. Similarly, we define the limits on the human appropriation of water (aggregate withdrawal or damping per year) on the basis of the structural and functional stability of ecological funds (defined over a much longer time scale) and the related land-use pattern.