If a local company is accused of dumping effluent into the water supply, then you'd better stock up on bottled water. Effluent is sewage or other waste that’s dumped into water.
Effluent traces back to a Latin word meaning “flowing out,” and as an adjective the word can still be used in that sense. An effluent stream is one whose water is continually flowing out of the ground, from a spring or other source. But the noun form of effluent refers to waste of some kind that’s been mixed with water. If effluent is released, it can contaminate a water supply. Gross.