The first thing you have to do is figure out the cause of the water spots and that can be several reasons. Spots could be an issue with your home's water quality, a problem with the water temperature or water pressure, or maybe it is your detergent. One way to remove most white-spot issues on your dishware is to add one or two cups of white distilled vinegar to the rinse cycle of your dishwasher. Some dishwasher manufacturers recommend doing this sparingly, as over time the vinegar, which is a mild acid, might damage the appliance. I have had this problem myself. I changed to a better dishwashing detergent. I prefer to use Cascade ActionPacs. They are so much easier to use than the old fashion powder or liquid detergents! Good Luck!
It is usually caused by undesolved powder detergent. You can try running a load with just your glasses and two cups of vinegar placed in a bowl in the bottom rack of the dishwasher. If this doesn't work the glasses are probably scratched from the prongs in the dishwasher. You can buy new glasses and start using with liquid detergent instead of powder. Hope this helps.