Install a dehumidifier in your crawl space if there is a problem with mild dampness in the air. This may be the result of moisture condensing when hot outside air meets the coolness of the crawl space.
Adjust the settings of the dehumidifier so that it maintains the moisture content of the air in your crawl space at a constant level. A dehumidifier with a control switch will go on and off automatically to maintain this level.
Empty the reservoir of the dehumidifier regularly to keep it working properly. Be aware that it will probably go on much more frequently in the summer than in the winter.
Apply high quality, tar-based waterproofing paint to the inside walls and floors of your crawl space to solve flooding problems. Remember that you will have to do this at a time when the walls and floor are dry for it to be effective.
Excavate around the outside of your foundation to resolve serious flooding problems. If your house was built without proper drainage or waterproofing on the outside of the foundation walls, this step may be necessary to fully solve your crawl space moisture problems.
Paint the outside of your foundation walls with tar-based waterproof paint after you have exposed them by excavating around the house. Install a plastic or rubber water barrier over the surface of the foundation walls for extra protection.
Install a 4-inch diameter drainage hose around the base of your foundation and run it either into a sewer or to a lower point of ground where the water can drain away from the foundation.
Backfill around the foundation and create a berm around the house so that water naturally flows away from the foundation walls rather than toward them.