My eyes will water when I am meditating. This is because I live in a very hot, dry, polluted area of the world and my eyes produce a lot of moisture to keep out all of that pollution and keep my eyes from drying out. When I am going about my daily life I am blinking, which normally sweeps away excess moisture. When I am meditating, I am not blinking (my eyes are closed) so the excess moisture builds up and starts dripping out as if I were crying.