What is the best definition of effluent in the context of water usage?

Effluent is best defined as water that has been used and will be recycled to varying levels of cleanliness. This definition emphasizes the nature of effluent as water that has undergone some form of use, typically in a domestic, industrial, or agricultural context, and is then processed for reuse. This can include water that may have been treated but is not necessarily fully purified, as it can still contain some level of contaminants depending on the treatment process applied.

In contrast, untreated water from sources like rivers or lakes refers to fresh water that has not been subjected to any significant treatment processes, which is not captured by the definition of effluent. Water that is completely purified does not reflect the original usage angle of effluent, as it implies a high degree of processing to remove all contaminants, positioning it at a higher level of purity than that typically associated with effluent. Stormwater collected for reuse is specific to precipitation runoff and does not encompass the broader context of reused wastewater, which is integral to the concept of effluent. This context helps clarify why the first definition is the most accurate representation of effluent within water usage discussions.