5 6Recycled water provides a viable opportunity to supplement water supplies as well as 7 alleviate environmental loads. This study examines the sources of recycled water and 8 discusses various end uses. This work focuses on reviewing the historical development and 9 current status of recycled water on a global scale with containing the evolvement of 10 wastewater treatment technologies, water quality guidelines and public attitudes. This review 11 also illustrates typical case studies of recycled water in a number of countries, including 12 Australia, Asia, the U.S., Latin America, Europe, the Middle East and Africa. These pilot 13 studies can be good examples for the future projects. The study identifies the good prospects 14 of further expansion and exploration of current and new end uses while emphasizing the 15 integrated water planning and management as well as challenging and tasks in the future. 16 17 28 29 30With the social development and population increase, water consumption has increased 31 beyond sustainable levels in many parts of the world (Dolnicar and Schafer, 2009). Uneven 32 distributed water resources, severe droughts, groundwater depletion, water quality 33 deterioration and climate change make the current water supply situation even worse. In 34 many countries, fresh water scarcity is already heavily emerged which is considered as the 35 single most important factor limiting socio-economic growth in the 21st century (Anderson, 36 2003a; Asano, 2001). According to International Water Management Institute's (IWMI) 37 report, Australia, California, the Middle East and the Mediterranean have been regarded as 38 high water stress regions (IWMI, 2006a). Likewise, the situation of water pollution and over-39 extraction in Asia and Africa is far from optimistic. Consequently, exploring alternative water 40resources has become an urgent issue, especially in these severe water shortage areas.
41Alternative resources include the capture and use of rainwater, stormwater as well as recycled 42 water and desalinated water, among which, recycled water provides a more constant volume 43 of water than rainfall-dependent sources. It also helps in alleviating the pressure on existing 44 water supplies and protecting remaining water bodies from being polluted. Thus, it is 45 increasingly being considered as a supplementary water supply (Huertas et al., 2008).