Dogs should drink a good amount of fresh, filtered water.
The amount of water your dog drinks depends on many factors, such as whether they eat dry food versus canned, activity level, weather, the kinds of treats they eat, and their emotional health. Keep in mind that your companion animal will drink more water eating kibble than when eating only canned food. Dry food only has 10% water while canned food has about 75%, thus dogs should drink more water when eating just kibble.
If you feel your dog is drinking excessively, please measure their intake and consult your veterinarian. Excessive water intake could signal the onset of an illness, such as diabetes or kidney disease.