A dog can survive two to three days without water, although this time frame varies based on the temperature and humidity of the dog's environment and its activity level.
In addition to hot, dry weather and high levels of activity, illness such as vomiting or diarrhea also increase a dog's need for water. Monitor any dog showing signs of illness carefully to ensure it does not become dehydrated. In temperate weather, a dog in good health needs to drink an ounce of water per pound of body weight daily. Pets should always have access to clean, fresh water that is changed regularly.