What size water bowl should you buy? Ideally, you should change your pet's water every day and wash out the bowl. You should run the bowl through a thorough was once weekly. After washing, make sure you rinse it well removing all traces of soap and cleaners.
As a rule of thumb, you pets bowl should hold enough water for him to drink for at least 24 hours, preferably 36 or 48 hours.
How much does a dog drink? As a general rule, dogs drink 20 to 40 ml of water per pound of body weight per day. This comes out to about 3 to 4 cups of water for a 20 pound dog.
So the idea bowl for a 20 pound dog would be 4 to 8 cups. Four cups is almost a liter so that is a big bowl! You may even want to consider a large bowel in the summer when environmental conditions are hot and humid.
As an alterative to one big bowl, you can also consider placing a couple bowls around your home.
For more information on water, please read Why Water is Important