Yes Dogs can become dehydrated quickly. Did you change his food? Some dogs GI tracts are very sensitive to changes in diets. I would first call the owner where you got the dog and ask if there had been a change and then ask a vet. Make sure he/she has plenty of water and try giving it some rice and chicken, or rice and hamburger. They literally sell it in the store and at the vets office now but I usually make it myself if my dogs get sick Good Luck
You can help the HubPages community highlight top quality content by ranking this answer up or down.