What are the rules of thumb for Turkeys going to water?
Do they go in the morning, evening, heat of the day?
Do they drink every day?
Is it ever worth trying to set up on them going or coming from a water hole?
Are they more likely to roost, feed, etc. in an area near some water or will they walk a long way to get a drink.

They do like roosting near water but that is more for feeling safe than drinking. I've found that unless you are hunting a very dry area with only certain areas to drink, its not a very effective way to hunt turkeys. Where Ihunt there are always puddles scattered throughout the woods and they will drink out of those just as soon and a pond. If it is dry where you are than I would hit it up mid morning.

I've found in dry areas around here that they'll head for water right off the perch in the morning.

I've had two tom turkeys drinking from our pond one time. Other than the creek or the small streams there isn't much place for them to drinkg around here.

Where I hunt, the turkeys will get a drink right before they fly up onto their roost in the evening. When there is a puddle out in a hollow in a field where I hunt, the turkeys become very predictable because they get a drink, and then walk into the woods and fly up into a field.