Dogs can become dehydrated within a few hours in hot summer weather, says veterinarian Cynthia Otto, DVM, PhD. In the case of extremely hot weather, older dogs, those with heavy coats and those suffering severe dehydration can die in less than a day.
Dogs have a very low threshold for tolerating dehydration. They experience severe symptoms after losing only 10 percent of their body water, says PetEducation.com. Although mild dehydration sets in quickly, it can be treated by putting the dog in a cool location and providing drinking water. Severe dehydration, marked by dry eyes, sticky gums, decreased skin pliability or diarrhea, requires veterinary intervention and may result in death.