Without proper grading, gutters, and downspouts, some of this water flows into the basement. The below-grade water table can also rise due to flooding or seasonal site conditions. This is why drain tile systems are recommended around basement walls even in sandy or gravel soils. Interior Moisture Sources Moisture is generated inside of basements from people and their activities.
Common sources are humidifiers, unvented clothes dryers, showering, and cooking.
When basements are finished, these activities increase. Another source that can be thought of as internal is the moisture contained in new concrete after construction. In a typical house, this can amount to 0.2 gallons per square foot of wall, and 0.1 gallons per square foot of floor. It takes many months to dry out and about three years to come into equilibrium with its environment. In the summertime, basement windows may be opened for fresh air.