Your crawl space should be dry at all times. Any moisture in the space can lead to major problems, such as mold or rot. Moisture can also attract both animal and insect space into the crawl space and eventually into your home. Determining why there is moisture in the crawl space is the first step toward fixing the problem.
The most common cause for standing water in a crawl space is poor drainage from the surrounding property. Your yard should slope away from your home, not toward it. A slope towards the house can deposit water in the crawl space, where low airflow and poor drainage can lead to standing water. Gutter issues, such as down spouts that aren't routed properly, can also deposit water beneath the house. A nearby AC unit can also lead to moisture if it isn't draining properly into a drip pan and is instead depositing its condensation into your crawl space. A crawl space expert can assess your lots slope, as well as check the guttering and nearby landscaping, to determine the cause of the drainage into your crawl space.
In areas with naturally damp soil or high water tables, such as in valleys, the moisture trapped in your crawl space could be evaporating out of the ground. In some cases, perforated drain pipes may need to be installed to route ground water and precipitation away from your home. A vapor barrier installed over the soil can also help eliminate evaporation from the ground. Further, since warmth speeds evaporation, it will be necessary to make sure your crawl space is properly vented so that it doesn't become too hot beneath your house.
Some home owners make the mistakes of completely enclosing their crawl space. This is typically done in an attempt to keep pests out of the space, but it has the side effect of trapping moisture inside the crawl space. A crawl space must be vented for air flow so that moisture can escape and heat doesn't buildup. Most home only need a passive ventilation system with sufficient vent openings. Your crawl space expert can install these and cover them with mesh to keep animals out. In some cases, you may need a fan powered system, as well, which will ensure that the air keeps flowing and moisture can't buildup.
Contact a crawl space repair service in your area for more help.