Basement dehumidifiers are designed to collect water from air in the basement and filter the moisture out of the house through drains. If the moisture stays in the air, it can rot the wood and provide a growing place for unhealthy and destructive molds. However, a basement dehumidifier is an expensive option and there are several alternatives you can consider instead.
If your basement or crawlspace does not already have vents, you can install them to take care of many moisture problems. Some modern basements are equipped with thermal seals instead of vents, but these seals can still allow moisture problems that vents can take care of. If your house already has foundation vents, check them to make sure they are not blocked. Foundation vents should be blocked in the winter to keep heat in and opened in the spring to let moisture out.
If you already have vents and they are not helping, consider adding more or enlarging the vents that you have. This option will be less expensive than installing a permanent dehumidifier. Wider vents leads to increased airflow and allow the moisture in the basement to escape more easily. Contact a contractor or construction specialist to make sure any vent changes are within building code and do not harm your foundation integrity.
For a simple measure that does not require any construction alterations, buy a hygroscopic compound from a local pet or home supply store. These materials excel at absorbing water. Look for calcium chloride grain bags that are used for de-icing or similar types of absorbent mixtures. Sprinkle the mixture in the bottom of a wide pan and leave it in your basement. The hygroscopic compounds will absorb water over a period of two or three days and turn it into brine. Dump the brine out and replace it with new salt. To speed up the process, use a fan to blow the basement air over the layer of calcium chloride to expose it to more water vapor.