Why is there more moisture occurring on my windows this winter ? There are a few reasons. It may be colder outside. You may be trying to save money by turning down your thermostat (too low). Your house is built better, there are no air leaks. You are not bringing in any fresh (dry winter) air. You are not using your bathroom fan when you shower and kitchen fan when you cook. You are not getting warm air flow across your windows. You have older single pain windows.
To understand what is happening we need to look at some basic environmental science. Cool air is able to hold less moisture than warm air. Therefore, when the warm, moist air inside the house comes into contact with the cool glass surface, some water vapor that can no longer be held by the cooled air is deposited on the glass. The point on which the water condenses is called the "Dew Point" If it is the inside face of the glass - you want to change that.
If you can have more warm air flowing across the inside face of the window this will keep the water from condensing on it's surface. Do not have drapes or blinds closed on your window - they will impede the flow of warm air.
Don't lower the inside temperature of your home too low. Colder air cannot hold the moisture and it will condense on your windows.
Turn on your bathroom fans when you are running water, showering or bathing. Turn on your kitchen fan when you are boiling water in the kitchen.
On days when the temperature is not too cold - open a window and turn a fan on. This will draw dry air from the outside in and push the moist air out.
Consider installing ceiling fans in large open areas - this will push the warm air back down and across any large windows.
Wipe off any moisture before the water leaks down inside your walls and causes mold. Eventually you will find a balance between comfortable humidity levels and too much moisture on your windows. Buy a hygrometer and try to keep your humidity levels around 35-40 during the winter months. (Hygrometers are instruments used for measuring humidity)