Operator terms · Wastewater
What is effluent?
Effluent is the treated water that flows out of a wastewater plant. It is what leaves after the collection, treatment, and disinfection steps, and it must meet the limits in the plant's permit before it is discharged to a stream or reused. Influent is the untreated water coming in.
Last reviewed 2026-08-03
Influent versus effluent
Influent is the wastewater entering the plant; effluent is the treated water leaving it. Comparing the two shows how much the plant removed.
Why permit limits apply
Effluent is discharged into the environment, so it must meet the limits in the plant's permit, such as BOD and TSS, to protect the receiving water.
Common questions
- What is the difference between influent and effluent?
- Influent enters the plant; effluent leaves after treatment.
- Where does effluent go?
- To a receiving stream or to reuse, after meeting permit limits.
- Why does effluent have limits?
- To protect the environment it is discharged into.