Cats in the wild rarely drink water from a stream - they rely on their prey for their fluid intake.

Feeding canned is a good start. But maybe a high quality food rather than a grocery store quality. If you can get some Halo canned cat food, that is a good one.

I haven't tried adding flavoring to my cats' food bowls. I do to my dogs all the time, they get chicken broth - low sodium, fat free, of course! LOL

He is hiding under a bed - does he have what he needs in that room? Food bowl, water bowl and litter box? Be sure the litter box is at least 10 feet from the food and water dishes. Is the door open? Maybe close it so he feels safe in the new environment and will come out and eat / drink at a relaxed pace. Make a routine of going in at set times, so he knows that between those times he will not be disturbed and can relax. Stress not only will dry him out, it will prevent him taking in what he needs. Just a few thoughts.

Good luck!