I'm going to travel to Hainan, and I want to ask if I can bring anything with water in my luggage.

Of course, you want to check it, right? Then there will be no problem. As long as it's not illegally checked, no one will check it. Even if they find what you are carrying through the machine, they won't rummage through your bag. Don't worry, but don't put it in your bag when you leave here. Even if you want to bring it, if you want to be inspected, you should bring cosmetics (liquid) at most.