If your dog is not drinking, in a fairly short period of time they can suffer from dehydration. Make sure your dog is not obtaining water from other places first—the toilet (put the toilet seat down), the cat’s or other dog’s water, the neighbors. Take water from home with you with a bowl when you travel, hike, or walk your dog so that they drink minimally from other sources that could make them sick. If you are certain your dog is not drinking or eating, call the vet…something could be wrong with their mouth, digestion, tumor, or other conditions.
If your dog is drinking lots of water, the first thing to pay attention to is if they are exhibiting any other type of symptoms, vomiting, not eating, lethargy, which may be indicative of a problem. Also, consider the volume of water they are drinking—do they drink small amounts frequently, or large amounts frequently as well as the weather (hot), and activity level. If they are drinking more than you think they should be, they could have diabetes, kidney problems, or an urinary tract infection as well as a number of other health conditions, all of which you should see your vet to determine the cause and remedy.