The dog vomits water with little white foam, which may be caused by improper diet, gastrointestinal disease, excessive hunger, etc. You can adjust the dog's diet and feed some probiotics appropriately. If the dog is not in good spirits, It is also accompanied by diarrhea, blood in the stool, lack of energy, not eating or drinking, etc. It may also be parvovirus or canine distemper. It is best to take the dog to the pet hospital for examination to confirm the cause.