I have dried water marks all over the car, and its especially annoying on the windows. These have been here since I bought the car, so they survive just a simple car wash. My question is, would a clay bar take these off, and then would the liquid glass I would use afterwards prevent this from happening again?

Here is the quickest and less costly first attempt.

Wash car then dry. Using a sponge and distilled vinegar apply to car and rub into surface. Do a small section at a time after a small test spot. If this is working complete the entire car then wash again. Be prepared to wax the car as the distilled vinegar will remove the wax.

The second attempt would be to machine polish to car or to use Scratch X by hand, wash, then wax the car.

Either way a few hours invested will fix the problem.

Good luck and post back if this worked for you.

another easy attempt would be to hand wash with dish soap (dawn) and claybar. you could also do some Maguiers precleaner before the claybar. then lg or wax or whatever finish you want on top.