Like all animals dogs cannot live long without water. A dog begins to dehydrate quickly without water. It will probably survive for three to four days without water. It can survive longer without food but not without water. A dog should normally drink water at regular intervals particularly when it is hot.
An adult dog can survive up to one to a maximum of three days without water, that's 24-72 hours. However, the length of time can be shortened if the dog engages in further exercise or physical exertion.
Depending on the circumstances, a dog can live as short as one day in very hot weather to as long as a week without water. Always be sure to keep your pet well hydrated and keep them out of extreme heat and cold. http://www.vetinfo.com/dogmaint.html