Burping is due to there been too much air in the stomach. The burp is the release of this air.
The cause of this is usually from eating or drinking at a rapid speed which pups love to do.
Giving your pup smaller amounts of water may help alleviate the burping. Also there a special dog bowels available that reduce the speed in which your pup can eat their food. There are knobs on the bowel which the pup has to eat around thus reducing the speed in which they can gobble. So if your pup eats and drinks slower the burping will be greatly reduced.