Dogs may drink more than usual for a number of reasons. Certainly in hot weather your dog will consume more water, especially if she has been active or out in the hot sun. However, some health problems can cause an increase in drinking too.
What's Making My Dog So Thirsty?
Any situation that might dehydrate your dog will lead to increased drinking. Diarrhea and vomiting take a lot of fluid from your dog that must be replaced. Fever or mild heat stroke can stimulate dogs to drink more than usual, as can bladder infections and mild kidney problems. More serious problems like kidney failure can also lead to increased drinking and urinating, or sometimes to a drop in drinking and little urine production.
Dogs need about 10 ml of water per pound of body weight daily for maintenance. Activity, environment, or health problems can all increase the amount needed. Ideally this will come from fresh water, but if your dog is ill, she may need fluid replacement by intravenous injections.
Certain hormonal diseases directly influence the amount your dog drinks. With diabetes mellitus, for instance, either the pancreas doesn't produce enough insulin or the insulin present isn't working properly to remove extra glucose from the blood. A diabetic dog therefore drinks more water to flush out the extra glucose.
Dogs that suffer from Cushing's disease (excessive adrenal secretions) or from Addison's (not enough adrenal secretions) may show increased thirst. Female dogs with pyometra (uterine infections) will often be very thirsty, and dogs with increased calcium in the blood are also very thirsty.
Monitoring and Treating Increased Thirst
Before you can notice an increase in drinking, you need to have a rough idea of how much your dog normally drinks in a day. Make sure water bowls are always available and refill them with fresh water at least twice daily. Just like humans, dogs prefer fresh, cool water. Pay attention to whether you need to fill the bowl up more often than usual.
If you are concerned about changes in drinking habits, be sure to let your veterinarian know. He may need to do some blood work, including special blood tests requiring a short hospital stay, to carefully measure exactly how much your dog is drinking and how much urine is being produced.