affluent, effluent

Affluent or affluent means wealthy or prosperous--
Some of our more affluent citizens have donated generously.
Would you believe that those poor people were once affluent and influential?

Effluent or effluent describes something that flows out--
The effluent waste should be contained, and kept out of the river.

Effluent may also mean something that flows out, such as a small stream from a larger one--
This is only an effluent, but we can follow it to the stream.
The town wants the effluent from the factory tested for poisons

Now that you know that, you can say--
"This was an affluent community, until toxic effluent polluted the water."