Waste water yes, intake water... Probably not. I used to swim in the seawater intake of a coal power plant. They need cleaning because a strong current encourages growth of filter feeding marine life and eventually that clogs the intake. I got the job when the guy who did it before me was swept onto the trash rack and drowned. When I say "swimming" I really mean walking. 30 kg of lead and a rope to shore tied to my harness (in order to avoid any unplanned staff replacement). Amazing dive. The life there is incredible. No humans are allowed anywhere near it for obvious reasons. The fish are plentiful, huge and unafraid. The growth is lush (at least until I rip it off and put it in a bag).