diarrhea in 18 month old

so for the last 4-5 days my son has had diarrhea but the last 2 days it looks like water and I don't know what it could be from.. he acts normal, doesn't have vomiting and hasn't had a fever.. about an hour ago I woke up (its 3:52 am here) and it was all over my bed, all over my side, and running down my sons legs so I had to give my son a bath and take a shower not to mention wash the bed off.. he's never had diarrhea like this before and I plan on calling his doctor later today.. how can I make sure he doesn't get dehydrated? I don't have pedialyte but do have Powerade.. would that be enough?