Water reclamation (also called wastewater reuse, water reuse or water recycling) is the process of converting municipal wastewater (sewage) or industrial wastewater into water that can be reused for a variety of purposes. Types of reuse include: urban reuse, agricultural reuse (irrigation), environmental reuse, industrial reuse, planned potable reuse, de facto wastewater reuse (unplanned potable reuse). For example, reuse may include irrigation of gardens and agricultural fields or replenishing surface water and groundwater (i.e., groundwater recharge). Reused water may also be directed toward fulfilling certain needs in residences (e.g. toilet flushing), businesses, and industry, and could even be treated to reach drinking water standards. The injection of reclaimed water into the water supply distribution system is known as direct potable reuse, however, drinking reclaimed water is not a typical practice. Treated municipal wastewater reuse for irrigation is a long-established practice, especially in arid countries. Reusing wastewater as part of sustainable water management allows water to remain as an alternative water source for human activities. This can reduce scarcity and alleviate pressures on groundwater and other natural water bodies.

There are several technologies used to treat wastewater for reuse. A combination of these technologies can meet strict treatment standards and make sure that the processed water is hygienically safe, meaning free from pathogens. The following are some of the typical technologies: Ozonation, ultrafiltration, aerobic treatment (membrane bioreactor), forward osmosis, reverse osmosis, advanced oxidation. Some water demanding activities do not require high grade water. In this case, wastewater can be reused with little or no treatment.

The cost of reclaimed water exceeds that of potable water in many regions of the world, where a fresh water supply is plentiful. The costs of water reclamation options might be compared to the costs of alternatives options which also achieve similar effects of freshwater savings, namely greywater reuse systems, rainwater harvesting and stormwater recovery, or seawater desalination.

Water recycling and reuse is of increasing importance, not only in arid regions but also in cities and contaminated environments. Municipal wastewater reuse is particularly high in the Middle East and North Africa region, in countries such as the UAE, Qatar, Kuwait and Israel.