Students today eh, if it bothers you that much I think the note idea to the invigilator is probably the best solution.
Spilling water on them is just ludicrous, and you'll be kicked out of the exam without question. Take some alcohol hand sanitizer, and use whenever you want.
Some people use aftershaves/perfume that I think smells, but complaining will get me nowhere.
Use the good ideas as above and get on with it, focus, and get a good grade.
Good luck with your A-levels.