They can die a horrible, painful death from UC, so if you can possibly take him to a vet, I really want to encourage you to do so.
Some things I've read on this forum & elsewhere about getting goats to drink more:
Have 2 pails of water-one plain & one with diluted gatorade, electrolytes, or apple cider vinegar.
Give fresh juicy fruits like watermelon.
Try warm water in winter.
Keep the water pails very clean.
Good luck & I sure do hope it's not UC,& that he feels better soon!
San Clemente Island Goats