You are on the right track by knowing that he is making excuses to get/keep you in his room. You say you don't give in to them except for the potty but really you do just by simply going into his room even if you don't give him that drink of water. Maybe if you set up a more structured bed time routine for him, it will answer all of his needs before the lights are out. Say his bed time is 8pm, about 45 mins (7:15) before bed, start a 5 min count down till it's time to get ready for bed and then do a couple of mins before the time. This will help him mentally prepare for going to bed and allow him ample time to get done anything that needs to be done. So then at 7:30, he gets in his pjs, brushes teeth, goes potty, reads a book, puts toys in closet, and any other excuses he would normal come up with get answered. Now say everything is done and it's only 7:50, leave a soft light on for him to lay in his bed and quietly look at books on his own for the next 10 mins. Then at 8pm, you or dad will come to his room to kiss him goodnite, turn the light off and that is it. No more trips to his room for anything, not even the potty. And you need to explain this to him as well when you lay him down with his book that you'll come back to check on him and after that it is lights out and you will not come back to his room any more. Or you can tell him that you or dad will check on him when you go to bed. Also, try to keep that hour before bed, calm. No rough housing, video games, cartoons, etc. Help his mind settle down so his body can relax as well.
A good book to read is 1 2 3 Magic. It has advice about how to handle sleeping and other annoying behaviours our toddlers like to throw at us!!
Good luck and stay consistant!
S.