When you get water on the inside of your window it is condensation, I assume you have double glazed windows ? Well on the inside of the unit is an aluminium bar called a spacer bar this is filled with thousands of tiny particles called desicant, desicant is an absorber of moisture. But will only absorb so much , usually double glazed units last for about 10 to 15 years , If you have moisture on your windows then I asume the desicant has seen better days
