First, make sure your cat is able to urinate; if not, he may have a dangerous urethral blockage, which is more common in male cats, and, a symptom of which, is refusal to drink. If this is the case, it's a medical emergency, and you'll have to do your best to find an ER vet center or other vet, to treat your cat.
If he is NOT having trouble urinating, you can dropper feed him with children's unflavored (clear) Pedialyte, if you're sure he's not diabetic. Use a 1cc sized dropper and give him 1 dropperful every 15 minutes for an hour, then repeat in 2 hours. If you don't have a dropper, use a medication syringe (without a needle), or a small spoon. Go in from the side of the mouth where there's an opening between the upper and lower teeth and squeeze a little at a time, waiting for a swallow, after each bit. Rub his throat gently to encourage a swallow, or blow on his nose. If he vomits, STOP!
Try your best to get your cat seen, ASAP. Look in your Yellow Pages under 'Veterinarians', for any listings with 'emergency hours', and call to see if someone will come into the office for you or make a housecall.
I hope your cat will be fine, once he's diagnosed and treated.