Rethinking water scarcity: quality matters
Current assessments of water scarcity primarily focus on water quantity. But as water quality issues are prevalent worldwide, we need to rethink the concept of water scarcity to include also the quality of freshwater resources available for different water use sectors and ecosystems. In today’s issue of Nature Geoscience Michelle van Vliet (chair group Water Systems and Global Change) and colleagues propose a new approach to estimating water scarcity that includes relevant water quality requirements per sector.
Today, one-third of the world population lives in areas of severe water scarcity or water stress. However, accessibility of clean water is fundamental for a wide range of sectors, such as irrigation, livestock, energy and manufacturing, as well for domestic uses. Over the past decades, water use has more than doubled. A growing global human population will place further demands on water supplies. However, both the availability and the quality of water resources will be affected by socio-economic and technological developments, climate change and increasing climate extremes such as droughts and floods. Urbanization and increasing volumes of untreated wastewater from households, industry and agriculture are all set to contribute to water quality deterioration, particularly in developing countries.
“Water scarcity is expected to worsen considerably in many regions in the coming decades,” says Michelle van Vliet. “But we must bear in mind that water resources for different uses will not only need to account for demand in water quantity, but also in water quality. Quality requirements for water depend on the intended use, such as water temperature, salinity, nutrients and other pollutants. For example, water temperature is a critical parameter for cooling water use by thermoelectric power plants. By contrast, for irrigation and domestic applications, salinity, nutrient and other pollutant levels pose more important constraints on usability. So it is essential to focus on the availability of water of suitable quality for specific sectors in water scarcity assessments.”
To obtain more appropriate estimates of current and future water scarcity for policy support and water management, the authors argue that we should shift our focus to the availability of water of acceptable quality for use in each sector, rather than looking merely at water quantity. For example, they found that including just water temperature in assessments of water scarcity leads to an increase in percentage of the world population under severe water scarcity from 34% to 37%, compared to assessments of only water quantity. And that is with just water temperature as quality parameter. And there are much more quality parameters critical for different water uses: salinity, nutrients, organic pollutants, pathogens, and other pollutants that could be included in this new concept for water scarcity. Michelle van Vliet: “In our concept we also take into account that in addition to human water-use sectors (such as irrigation, domestic water use and energy generation), freshwater ecosystems also depend on water of good quality to maintain ecosystem health.”