It's a phase, but he will likely need help transitioning through to the next developmental stage. You can help by giving tools to deal with the things he can handle independently and lots of love/empathy for the struggle.

We found some success combining your current approach with some light use of social stories (telling stories/reading books about others with the same worries, etc). Sometimes it was enough to say things like, "I wake up thirsty too. When I was your age, grandma gave me a special water bottle/cup/whatever works for you. Every night I filled it up when I brushed my teeth and kept it by my bed. Remember the story I told you about the magic flashlight grandpa gave me when it was too dark to go potty by myself? Well, when I was thirsty, I would turn on my flashlight and take a drink out of my special water bottle and I could go back to sleep! Now I'm a grown up, and I still have a special water bottle that I fill when I brush my teeth at bedtime, and I still wake up and take a drink at night when I need to." Sometimes we would take a special trip to the store and they could pick out their special bottle; sometimes they already had something that would work for the situation.

I mean, we would have to do several iterations of this, along with a fair amount of just letting them sleep with me at times. When it got rough, I could set up a sleeping area for them to use, but the idea there was they wouldn't wake me, just be able to feel better by being close. By about 7 yrs all three of our kids were sleeping through 95% of the time. There are still the occasional nightmares, yucky feeling tummies, etc. Maybe it's more like 98:2 vs 95:5.