Alot depends on the weather and their activity. Mulies are not habitual and just because they watered today in a spot, doesn't mean they will be back in the A.M. Most often though, mulies will share the same travel routes, I would look for travel routes and concentrate your efforts there through glassing. It could cut out alot of country that you need to cover and or glass.

Water holes could be somewhat productive as I have watched alot of deer water while waiting for antelope. I still wouldn't count it out, good luck!!!!