Everytime. I go out of my way to force out farts and wee wee while I'm in a swimming pool.
One time in school swimming class I forced a fart too hard and a bit of shit came out. I panicked because it would end my rep there and then.
Luckily I'm a good bullshitter (and a normal shitter) so I saw the kid in the other class from the year (who had downsyndrome). Instantly I deflected it "did you see that - he just shit in the pool?" dull cunts believed it and he took the abuse, it was open season back then on disabled kids.
Shat in a pool once when I was a kid. It was quite solid, so I hooked it out of my trunks and set it floating in the gutter that ran around the edge of the pool.