Be very very careful with Muriatic acid... it is used in stripping chrome (which might be around the windows and trim). The warmer the acid and chrome, the easier it strips the chrome. Removing water spots on glass really depends on how deep the water spots have etched the glass. Claying the glass is extremely safe and removes mild blemishes from the surface. You can also compound the windows just becareful of any protective films. Acids can work also but need to be done with care. Vinegar as a water spot remover has been around for a long time and is proven for mild spotting. Some companies make water spot remover, some for paint, some for glass, some for both. NOT ALL, but most of these are basically diluted wheel acids. They do work but be extremely careful when using them. Do not allow them to dry on the surface. Rinse the acids off often and thoroughly. Make sure they are not only rinsed from the window and paint but also the trim and wheels. Since most cars come from the factory with aluminum wheels keep in mind that these acids can stain aluminum. Most of my customers do not offer a guaranty, only a "we will do the best we can" and do the job within what they feel are safe limits. If this is unsatisfactory they let the customer take the car somewhere else to become someone else's problem. I hope this helps.
Danny