Thanks for the tag,
@Weeg
First of all, I think you having other drinking water sources aside from swimming water is important since ducks poop in their swimming water. I just use water buckets, and change them 2-3 times daily.
My ducks do have infectious bronchitis. The way to get a diagnosis is with a blood test at a vet. When ducks first contract the virus they can have respiratory symptoms, and after that the virus lives in the egg shell gland indefinitely. If you have it/think you have it you might want to consider keeping a closed flock (no birds in or out) so that you don't spread it or condemn new birds to life with the virus.
I don't actually know anything about chickens. I only have ducks. But my avian vet told me that there is no cure for infectious bronchitis, only supportive care for the symptoms.