Recycling of effluent water from urban water-supply systems is often a more sustainable water source than increased use of surface sources, groundwater sources, and desalination. However, water-supply organizations (WSOs) often do not take full advantage of recycled water. Although recycling water for direct potable use is efficient, public concern with safety has tended to cause WSOs to favor other uses for recycled water. This study examines patterns in the degree of utilization of two main indirect uses of recycled water: dual-reticulation systems and groundwater recharge. Drawing on case studies of four U.S. cities that are leaders in the use of recycled water, the study identifies conditions that favor the choice of one option over the other. Where cities are concerned with groundwater recharge of potable water supplies, they tend to prefer non-recycled water if available for recharge projects. However, where non-recycled water supplies are limited, recycled water may be prioritized for aquifer recharge. Otherwise, the preference is for use by large industrial partners such as power plants or for exchanges for higher-quality potable water resources with rural systems. In contrast, dual-reticulation (purple-pipe) systems for direct nonpotable recycling face steep economic and technical challenges.

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