Even with the popularity of double-paned windows, you can still find many older homes with single-paned glass windows. The lack of insulation within these windows leaves them susceptible to drafts, leaks, and seal corrosion. You can always replace the window to fix the problem, but the labor and product costs are usually a bit too high for the average homeowner.
As an alternative, you can always place acrylic plastic sheeting over your drafty single-paned windows. This is something you can easily do on your own, but labor costs should be pretty reasonable if you decide to hire a handyman. First, purchase a clear acrylic sheet that fits the dimension of your window, and line the edges with a thin magnetic strip. Next, place another magnetic strip around the border of the drafty window you plan to insulate.
During inclement weather conditions, place the acrylic glass over your window by lining up the magnets and pressing them together. This will create a pretty tight seal that will keep out moisture, cold, and excessive heat.