Once the water accumulates around your foundation, it works its way inside through cracks, joints and porous material. A pro cure can cost from a few hundred dollars to many thousand. But even if you're knee-deep in water, don't call your banker yet. It happens when moist, warm air hits cool foundation walls or uninsulated cold-water pipes, dampening carpets, rusting appliances and turning the basement clammy. In crawl spaces, condensation encourages wood rot and insect attack, and can buckle and delaminate plywood.
Condensation is easy to confuse with runoff or subsurface water.
To tell it from the others, tape foil over damp spots and check it after a day. If moisture forms on the outer foil face, water is condensing from the air. If moisture forms on the foil underside, water is seeping in from outside. Start with the easy stuff. If you have a full basement, air it out by opening windows and running fans.