
I had a dog that would vomit if he had a cold drink when he was warm after coming in from a walk, awkward if he found a river when on a walk as he would have a good drink then promptly throw it all back up a again.
The only thing we could do was not to let him drink a vast quantity all at once and warm the water so it wasn’t a sudden cold dollop onto his stomach.
I don’t know whether this is a similar thing, but try giving him warm water and see if there is any difference