Do you have any TT CTN bottles at all?
If so, TT do a non spill sippy cup that has interchangable handles which will fit on the CTN bottles.
What we done to begin with is put the handles on her milk bottles and let her get used to holding the handles.
But as some of the others have said, non spill cups were a no go and she wouldn't drink from them, she'd only chew on them.
As soon as we gave her a free flow one she was away, drinking like a pro! Honestly you wouldn't believe it. But then she would never drink water out of a bottle but out of a sippy cup she loves it.
Another thing I've found is that she watches me sooo intently whenever I drink. I have read before that getting a sippy cup yourself and letting LO watch you drink from it can help and knowing how much Violet watches me drink, I can quite believe that.
If he still won't drink from a cup then personally I'd still offer it to him (to explore and learn) but continue to give him water in a bottle if you're worried about dehydration.