Well, now I'm beginning to wonder - my mom has made him drink tons of water today and now he seems to be going fine.

Sometimes I think I just overreact, but no matter what I still think 16 hours is way too long even if he hasn't had enough liquids.

Thanks to all of you and I will keep you posted.

NO you were right to be concerned
 

16 hours is way too long to go without relieving the bladder. Keep an eye on him and keep us posted.