Water spots on a windshield can be removed. Just purchase a bottle of white vinegar. Now soak a terry cloth in the white vinegar and then squeeze out the excess. Now rub the spots with the cloth until the spots are gone. Wipe the area clean with a terry towel soaked in warm water. Dry the windshield and it will be spotless.

Hmmm, the best way is to just get a new windshield. Once you get water on a windshield it is ruined.

Water spots are usually from stuff in the water, ie. minerals and/or like Calcium or salt. If you try a vinegar solution it might work.

Vinegar.

Get clay bar