What time did the pool close to the public and would you have normally used it after that time and was there notice given? I think some context is needed here.
If there was notice of the closure prior and if it were for just one night, I would move on and forget it. Knowing that hotels have some flexibility with resort fees if you feel that strongly about it, ask for a waiver for that day and explain that they failed to deliver the other benefits, assuming that you've already let someone know you haven't received your water.