A dog that only drinks water but does not eat may be caused by internal parasites, gastrointestinal discomfort, canine distemper, parvovirus, cold and fever, or other diseases. You need to observe whether the dog has other symptoms. If there are no other symptoms, , you can first feed some probiotics to regulate the intestinal tract. If there is poor energy, vomiting, diarrhea, blood in the stool, etc., it is best to send it to the pet hospital for examination and treatment immediately to avoid delaying the condition.