Global water scarcity including surface water quality and expansions of clean water technologies

Water scarcity threatens people in various regions, and has predominantly been studied from a water quantity perspective only. Here we show that global water scarcity is driven by both water quantity and water quality issues, and quantify expansions in clean water technologies (i.e. desalination and treated wastewater reuse) to 'reduce the number of people suffering from water scarcity' as urgently required by UN's Sustainable Development Goal 6. Including water quality (i.e. water temperature, salinity, organic pollution and nutrients) contributes to an increase in percentage of world's population currently suffering from severe water scarcity from an annual average of 30% (22%-35% monthly range; water quantity only) to 40% (31%-46%; both water quantity and quality). Water quality impacts are in particular high in severe water scarcity regions, such as in eastern China and India. In these regions, excessive sectoral water withdrawals do not only contribute to water scarcity from a water quantity perspective, but polluted return flows degrade water quality, exacerbating water scarcity. We show that expanding desalination (from 2.9 to 13.6 billion m(3) month(-1)) and treated wastewater uses (from 1.6 to 4.0 billion m(3) month(-1)) can strongly reduce water scarcity levels and the number of people affected, especially in Asia, although the side effects (e.g. brine, energy demand, economic costs) must be considered. The presented results have potential for follow-up integrated analyses accounting for technical and economic constraints of expanding desalination and treated wastewater reuse across the world.

Automated summary

Global water scarcity is influenced by both water quantity and quality issues, and increasing investment in clean water technologies is crucial to reduce the number of people affected. Considering water quality factors can raise the percentage of population suffering from severe water scarcity in heavily affected regions. Excessive water withdrawals and polluted return flows contribute to water scarcity and degraded water quality in severe water scarcity regions. Expanding desalination and treated wastewater reuse can effectively alleviate water scarcity levels in Asia, but potential side effects must be carefully considered.