Don't worry about the detractors, they just want to start an argument. Chuck, in particular, thinks that water should never be in play on a hole lest one beginner lose their only disc and become so disgusted that they never play disc golf again.
The hole that you put the concrete in should be 24" deep and 6-8" in diameter. So here are some of suggestions:
1. Buy a cardboard cylinder that is 24x8" and pour the concrete into that, letting it set around the base of the pole or the sleeve depending on which you are using. Then, dig the hole at the location and put the preformed base (with cardboard cylinder removed) in the hole and tamp in dirt and sand around it.
2. Build up the area where you will put the basket so that digging into the built-up ground will allow the hole to be dug without reaching the water table.
3. Use a 24" long piece of 6" pvc drain pipe with plastic securely taped to the bottom. Dig the hole so that the pipe fits very snugly (tamp in sand around it to fill any voids) and then install the pole into pipe with concrete.
Any time I have run into this problem, I have just put dry mix into the hole and used the existing water for the concrete. I can take out some water if there is too much, but I've never had to.