I've fed poolside on a seat in my cossie. I deliberately had a cossie that was easy to pull aside, and baby's head covered the rest of the breast. It was a photo session for my 2 year old, and I was not wasting the fee I'd paid by going on a slow, cold walk round the corridors to the changing room. The pool was not a practical design for sitting, but had it been that style, it would have been a warmer option.
I exposed far more in the communal family changing room. Yes, two whole breasts, and two whole buttocks as clothes were going on and off. If you are going swimming, you have to accept that you will see more flesh than is usual. No one seems to question teenage girls preference for string bikinis that leave very little uncovered.
The hygiene of the water is no different as unless you shower and wear nothing that has been in contact with pool water, it is on your skin anyway. When I've gone to laned swimming sessions, it is normal to take a sealed plastic water bottle for hydration. I wouldn't feed a bottle of milk in a pool for the practical reason that I'd have to get out to get it, which removes the convenience factor. I'd botte feed a baby in a car, as that is practical, as a back seat passenger, I can reach and hold a bottle. I could not breastfeed in a moving car as there is no legal, and comfortable way I could lean my breast to baby while leaving it secured in the car seat. Comparisons of where you would breast and bottle feed are not always equal.
Since the story of feeding in the pool last year, I can't think of any reason against that people offer that can't be debunked.