The practice of treating and reusing wastewater for beneficial purposes such as irrigation, industrial cooling, groundwater recharge, and in some cases, potable water supply. Water reuse is an increasingly critical strategy for water-scarce regions.
Water reuse (also called water recycling or reclaimed water) involves treating wastewater to meet specific quality standards for subsequent beneficial use, reducing demand on freshwater sources and wastewater discharge to the environment. Non-potable reuse applications include agricultural and landscape irrigation, industrial process water, cooling tower makeup, toilet flushing, and environmental enhancement (wetland and stream flow augmentation). Indirect potable reuse (IPR) introduces highly treated wastewater into an environmental buffer such as a groundwater basin or surface reservoir before eventual withdrawal for drinking water treatment. Direct potable reuse (DPR), where advanced-treated wastewater is introduced directly into the drinking water treatment process, is practiced in Windhoek (Namibia) and increasingly in Texas, with major facilities planned in California and other water-scarce regions. Advanced treatment for potable reuse typically includes membrane filtration (microfiltration, reverse osmosis), advanced oxidation (UV with hydrogen peroxide), and in some cases, activated carbon adsorption. The state of California adopted comprehensive DPR regulations in 2023, a landmark for U.S. water reuse policy. Water reuse offers significant benefits for water supply reliability, energy savings compared to long-distance water conveyance, and reduced environmental impacts of wastewater discharge. Public perception, sometimes called the 'toilet to tap' stigma, remains a challenge for potable reuse projects, though education and transparent communication have improved acceptance.