Balancing the needs of all services provided by global water resources

Global assessments of water use tend to focus on the supply side, where data on physical hydrology provide an apparently (but often questionable) secure underpinning. However, one difficulty with this approach is that it struggles to deal with the issues of multiple uses of water and of treatment and recycling. Another is that global analysis offers little guidance to water policy and management, which invariably and necessarily act at more local scales. An alternative approach is therefore to evaluate demand for the goods and services offered by water, to both human beings and to ecosystems, and then to map these demands back onto resource flows. This paper describes the sources (precipitation, surface water and groundwater) and the uses of water in delivering all of its services (including its provisioning of environmental services), and uses two Sankey diagrams to visualise this system. The results stress the need for an integrated assessment of all water sources and services, simultaneously considering human and ecosystem needs, and highlighting the need to improve human water-use efficiency and productivity rather than lazily invading further the needs of ecosystems on whose additional services humans rely