Water Reuse in Arid Zones

Given the current demographic trends and future growth projections, as much as 60% of the global population may suffer water scarcity by the year 2025 [9]. In addition to water scarcity, water quality deterioration is expected to intensify in resourcepoor countries in dry areas, due to human activity and climate change. It is projected that water scarce countries will have to increasingly rely on alternative water resources such as wastewater to narrow the gap between water demand and supply for agriculture [16,18,19]. There are large gaps between developing and developed countries as well as lowand high-income countries for managing wastewater generated within their boundaries. High-income countries on average treat 70% of the generated wastewater, followed by upper-middle-income countries (38%), lower-middleincome countries (28%), and low-income countries, where only 8% of the wastewater generated is treated [31]. Wastewater treatment and use and/or disposal in the arid and semi-arid regions of developed countries, such as western North America, Australia, and southern Europe, are motivated by stringent effluent discharge regulations and public preferences regarding environmental quality [13]. Treated wastewater is primarily for irrigation, given the increasing competition for water between agriculture and other sectors [31,34]. In developing countries, wastewater treatment is limited, as investments in treatment facilities have not kept pace with persistent increases in population and the consequent increases in wastewater Manzoor Qadir United Nation University Institute for Water, Environment and Health (UNU-INWEH)