If you notice your windows have streaks, smudges, and dust shortly after you have cleaned them with store-bought cleaners, this is because they leave a waxy buildup. Instead, according to the Queen of Clean, Linda Cobb, a mixture of 1/2 teaspoon of liquid castile soap, 3 tablespoons of white vinegar, and 2 cups of warm water in a spray bottle will leave your windows sparkling clean and clear for months! If your windows are especially greasy, I have used Dawn dish liquid instead of the castile soap and it leaves even my glass tabletops clean and clear for a longer period of time!