If you feed raw, they will drink less water as they get it from the food.
I will say- my dogs until we put in a new water treatment in the house, only drank bottled water- anything else was totally unwilling. ..
1/2 gallon sounds like alot of water to me, but would not be for shepherds- so I am taking your word for this- that is not much water. Have you tried adding a little bit of plain pedialyte if you are worried about this? Also one more thing- two of my dogs will only drink cool water- below room temp.. but none of them will touch warm water or too cold..
And to relieve your mind a little- most serious medical problems the sign is "excessive drinking" - not drinking what you perceive is too little..