[Paridel]

Polio is mostly contracted through fecal-oral transmission. When it was a major problem in the US many mothers wouldn't let their children swim in public pools. It turns out they were right to do so - small children fouling public pool water was a major decease vector.

-paridel

[hellbender]

It wasn’t urine which spread polio, but fecal contamination. Any responsible municipality with a surface water supply, like a reservoir, is going to give the water filtration (which will remove many pathogens), possibly coagulation with chemicals to help remove particles, followed finally by disinfection, usually with chlorine. One man urinating in the reservoir is completely trivial.