This is a common question people ask us, but it isn't a simple question. Many people would say a dehumidifier, and while they would not be wrong, they definitely would not be completely right.
To control moisture in a crawlspace, you must prevent it from entering in the first place. We do this through CleanSpace, a vapor barrier that is sealed when installed.
The second step is to install a SaniDry Sedona dehumidifier. Now that most of the moisture is stuck outside the crawlspace, the dehumidifier can help to regulate the humidity level.
WaterGuard is used for the floors, and CleanSpace wall liner or Foam X is used for the walls.