I have heard bad things with trying to thin out latex paint with water to get it to work with a decent HVLP. To get the right constancy I am told that you need to use floetrol
As you atomize the latex with water it breaks apart and you get globs of paint rather than a mist. I have never tried to do latex. What size needle do you have in your gun? I have a .75mm, 1mm and a 1.5mm. but I have again heard from some that trying with less than a 2mm can get funky results unless you can really thin out the latex.