Generally speaking, the hard water stains on your eyeglasses cannot be removed with your average cleaner. However, you can use vinegar and baking soda to clean them. At first, you should mix up the vinegar and baking soda to make them a paste. Then apply a little paste on the hard water stain area. Use a sponge to rub the stain area in a circular motion for 10-15 minutes. Finally, use a damp towel to wipe off the paste.
You may pay attention to the following points. Firstly, sunglasses are easy to be coated with dust. Wipe away the mirror with soft cotton cloth and then wipe it with the professional cleaner or wash them with clean water. Secondly, mirror up when you place sunglasses and do not wear them on your head. Thirdly, avoid by all means to place sunglasses in high temperature environment for a long time. What's more, avoid contacting with things containing chemical compositions such as perfume and pesticides. At last, put you sunglasses in the special glasses bags if you do not wear them for a long time.
You can wet your eyeglasses or rinsed the lenses in a warm water, and use a pieces of eyeglasses cloth to wipe it out gently as long as the hard water stains out. If it doesn't work, you may use soap to clean the lenses. And clean the lenses again. If it is work, you may have to take your eyeglasses to an optical store to have them clean your eyeglasses.