Correctly, you have thermopane windows (two layers of glass filled with gas) It sounds like one of these has failed, and formed moisture in between the two layers of glass.
Most thermopane windows have a warranty against this type of failure. Some of these warrantys can be quite long, and pass from owner to owner. Anderson for instance has a 25 year warranty.
I would check with the representative in your area for the windows you have to see if they are covered.
Otherwise, I'm afraid you will have to replace the window to get rid of the moisture. There just isn't a good way to repair a failed thermopane once it has started to leak.