What is effluent in the context of water treatment?

Effluent refers specifically to the water that flows out of a treatment facility after it has undergone various treatment processes. This water is typically the final product of wastewater treatment or treated water that may be released into the environment, returned to a water body, or reused for various purposes. Understanding effluent is critical in water treatment as it represents the outcome of the treatment process, reflecting the facility's ability to remove contaminants and meet regulatory standards for water quality.

While the other options relate to different aspects of the water treatment process—such as inflow into a treatment facility, water that has undergone treatment for the purpose of reuse, or stored water in a reservoir—they do not accurately define effluent. Instead, they emphasize different stages or locations within the overall water management cycle.