Water is deadly in the right areas a couple thing's I'd mention.
1. A tree is much better than the ground. In a tree, you can pretty much do anything without getting busted. It would take alot for them to look up at you, alot.
2. Make sure you know what the thermals are doing near the water. Set up on the side or downwind side if possible. Contrary to what many think, elk do not come to the pond from downwind all the time but it's always best to play that side.
3. If you can tolerate a little height, and the angle allows, get up 15+ feet. Depending on terrain, any downwind elk coming in may make it without winding you. Big "Maybe" there.
4. Time of day, best times will be mornings, and evenings. First and last two hours reason being is the wind should be about dead, and your're normally dealing with thermals at that point, and not winds.
5. I guess it really depends on the areas, but I find elk are not cautious at all coming to water. Many times they are running in. Seriously, running. I've seen them come down a ridge so fast to the water it was liked someone spooked them on the other side.
6. I always say take the first good shot, but if they commit, you have all the time in the world normally. Relax.
7. At times I will call, not much, a calf or mew etc. Mostly if I see elk out of range.
8. Lastly, when you climb the tree, and if in range of the waterhole, bring a couple decent sized rocks up with you, baseball size. When you see a bull pass out of range and you throw a couple mews his way and he doesn't respond, out come the rocks and throw them at the water. Trust me on that one.
Good luck.