It depends some on what he is eating. If it is wet food - he doesnt need to drink so much. It it is mainly dry food - he should drink quite a lot.
Try with several drinking cups in different places. Made of different materials ceramic-clay, stainless steel, even one in plastic. Fresh water in most, but in one stale water. (some cats prefer stale water!).
I presume there are drinking fountains for cats in US too?? feks Drinkwell or Cat-it. Many catowners witness theirs cats are now drinking much and freely and with enjoyment.
If you forcefeed (necessary sometimes, feks in hot summers), use a syringe - without needle of course, or eyedropper. In the corner of the mouth ACROSS the mouth, NOT down the neck. Best and easiest is if one holds, one forcefeeds the water.