One very obvious source of moisture and/or water in your basement is rainwater. During a hard 2 "- rainfall, a 1,000-square-foot roof will collect about 250 gallons of water, dying to get into you nice dry basement. If you have four downspouts, that averages out to about 63 gallons (240 l) per downspout location. Check your roof thoroughly for leaks and repair them as soon as possible. The longer you let the problem occur, the worse the damage will be.