Excessive thirst or "polydypsia" in dogs is a symptom of several potentially more dangerous medical problems. Unless your dog's drinking problem only lasts a couple of days or has an obvious external cause (medications, forgetting to fill the water bowl, hot weather, exercise), it's a sign to make an appointment with your veterinarian.
~ Cushing's (Hyperadrenocorticism)
Cushing's syndrome is a relatively common disease in older dogs which is caused by the adrenal glands producing an excess of steroid hormones. Excess water intake, and increased and almost uncontrollable urination are the major symptoms, along with increased appetite, skin and coat changes and a loss of energy. Cushing's can occur in any breed, but Boxers, Poodles, Dachshunds and Boston Terriers are more likely to develop the disease.
Adrenal -dependent Cushing's is caused by a tumor on the adrenal gland. Pituitary-dependent Cushing's is caused by the overproduction of adrenocorticotropic hormone. Iatrogenic Cushing's is the most common form and is caused by excessive cortisone usage.
Diabetes isn't a common disease in dogs (an estimated .5% of dogs have the disease), but it is a potentially serious problem. Diabetes is caused by an insulin imbalance - too little causes hyperglycemia, which is the most common form in dogs. Obesity is a major contributing factor, as well as hyperthyroidism and Cushing's. Some breeds are more pone to developing diabetes, including Dachshunds, Miniature Schnauzers, Toy Poodles, Pomeranians,
Other symptoms include increased urination and weight-loss. If left untreated, kidney disease, cataracts and neurological problems can also develop.
Diabetes can often be managed with diet and exercise, but some dogs may require injections. In Type II diabetes (non-insulin dependent), reducing a dog's weight may return the insulin production to normal or near normal levels.
~ Kidney Disease or Failure
Basically, the kidney cleans wastes from the blood, controls the retention of salt, calcium and phosphorous and the retention of water. When the kidneys start to fail, they no longer efficiently process wastes or concentrate the urine, and the dog drinks and urinates more frequently.
Kidney disease can be caused by a tumor, physical trauma, deprivation, infection or toxins (antifreeze, heavy metals, rat poison, certain plants). Excessive water intake will stress the dog's system and can also lead to chronic kidney problems. A severe bladder infection may back up into the kidney's causing a kidney infection, which left untreated can turn into a chronic problem. Some breeds (Shar-Pei, Basenji, Lhasa Apso) are more prone to kidney problems.
Dogs require two to three times more water than food on a daily basis. This means if you feed your dog two cups of food a day, they will need four to six cups of water - more if you feed dry food, if your dog is stressed, if the weather is very warm or dry, or if your dog is very active. It can be easy to under-water your dog, especially if you're working on housebreaking issues, however it can lead to dehydration and develop into a pattern of obsessive drinking.
Abused or abandoned dogs who have been left for days without sufficient water may develop a drinking compulsion, emptying every water dish in sight and even lifting the toilet seat if they can't find water elsewhere. If you have a heavy drinker, talk to your vet to ensure their kidneys have not already been damaged, turning a mental problem into a physical one.
Behavior modification is the only way to help a compulsive drinker. Make sure they have access to small amounts of water at all times - use ice cubes to provide water if you must leave the dog for any length of time. You're helping them to get over their fear that they won't have water when they need it. Manage the excessive urination with more frequent trips to the yard or by using piddle pads.
Medications, in particular steroids, can also cause excessive thirst. Steroids are commonly prescribed to treat allergies, kidney problems and excessive itching, but they do have serious side effects, including increased thirst. Long-term steroid use is a contributing factor in Cushing's, which also causes excessive thirst.
While having to constantly fill the water dish (and clean puddles) may be frustrating, taking care of an underlying medical problem and managing water intake can make your life - and your dog's life - much happier and much more comfortable.