BPA, birth control/estrogen in water, and increased obesity rates would be my guess.
Is that actually a thing? I didn't find any sources definitively showing it was enough to warrant a concern.
they pee and flush
this water gets processed and re injected back into the pipes
if you make the mistake to drink the tap water where they re purpose it from the canalisations, you just drink birth control water.
From what I was reading, this seems to be an anti-BC talking point, but I couldn't find any evidence to suggest that any estrogens in tap water is caused by BC.