Just before you get into moab. You cross the river on a bridge. Directly at the end of the bridge is a turn left. This turn takes you to big bend and through the canyon. a few hundred yards down the road there is a pull off with a spicket coming right out of the wall with fresh running water. SOak it up!
Texico in Monticello (across from the peace tree) will let you fill up. take the road over the mountain (blue mt road ?) and save about 10 miles with great views of canyon lands and the creek.
The spring is called "Matrimony Spring" and is on some maps. A historical research study proved that drinking it can actually improve your climbing ability.
I was on a 2 week roadtrip this summer and filled up at Matrimony Spring every morning while staying in Moab. We never had to wait in line and the water is fantastic.
Darren - not doubting you had to wait in line, I probably just got lucky and went early in the morning.