How do you get hard water marks off windows?

Make a solution of white vinegar and water 50/50 and add a dab of dawn and jet dry.

Wet a used fabric softener sheet and wipe the window with it. Then dry.

We use Zani Clean High Performance Cleanser, it is safe to use and works wonders, good for glass cook tops too!

I have REALLY hard water in my area. I use straight white vinegar, rinse with warm water and dry immediately with newspaper. I also have my windows professionally serviced (as they also clean and mend screens if necessary), every Spring and Fall.

If these exterior windows and none of this works, you probably have etching usually caused by acid rain.