How do you get your cats to drink water?

Part "give me the crazy steps you've gone through so I can try" and part "I just need to vent".

I have a cat, Oliver, who does not drink enough water. He's having some litter box issues and that's part of it. We have a water fountain, a bowl with a waterfall to keep it moving, a regular bowl, and an elevated bowl that dumps the water every 3 hours so it's fresh. He doesn't have any interest in licking the water from the bathtub.

We thought it may be a territory thing. All our water bowls are on the main level, where the other 2 cats also spend their day. One of those cats drinks a butt load of water (medical issues) and the other likes to play in the water. So we put one upstairs in the bathroom, as Oliver is a bathroom cat and easily spends a couple of hours in there every day with us. He has no interest there either.

I added fish oil to the water, no interest. I added water to his dry food and he refuses to eat it. He is on a prescription diet so only has one option for wet food and he doesn't really like it. Because of that diet, he's not supposed to have any of the soups or churros.

So at this point, I'm at a loss on how to get water into this cats body. I'm open ideas. And also for frustrated rants from other owners with these same issues.

I do feel this may be karma for how difficult it was for my mom to convince me to drink water as a child.