Warm air can carry more moisture than cold air.
When the warm wet air in your rooms comes into contact with the slightly cooler window glass - moisture condenses out on the colder surface.
There are some things you can do to reduce the problem but you might not be able to cure it completely.
Keep the steam down from bathrooms and kitchens - close doors and open windows when you're creating steam.
Ventilate the rooms you occupy at night - much of the morning moisture will come from your night-time breathing.
Mop up the condensation when you see it else mould will form.
http://www.rotherham.gov.uk/info/141/housing_repairs-council_property/1901/preventing_condensation_and_mould/1
Peccavi, January 2013
