On: A washing machine for human beings, from 1970

[toast0]

Part of processing is often adding clean water; to the extent that you've already done it upstream, the treatment plant can add less.

[eru → toast0]

Maybe. Though when you add clean water upstream that usually means water clean enough to be fit for drinking (because that what comes out of your tap.)

When they dilute at the treatment plant, they can use somewhat dirtier clean water.