But in all seriousness, just keep an eye on him. If he behaves normally and displays no other symptoms, he's probably ok. He'll probably learn not to breathe water in like that again. Our dragon puts his head under during baths and you can see he literally chugs water.
I agree, a lot of them love to dip their heads under water to drink. Some have a terrible time
with aspirating water because they get overzealous about drinking & will end up having some
trouble.
I would suggest upping his basking temperatures by a couple of degrees for a week or two in
case he did have any water go down the wrong way. It will just boost his immune system by
a little to help out.
How is he doing today?