1. Your water supply is leaking someplace. How is your water bill? Is it a lot more than your neighbors? (This is a good way to introduce yourself, bring along a 6 pack.)
2. How is your home landscaped? If you have any berms, plantings, etc that could direct water towards your foundation, this can be a problem. All of your grading around the house should direct water AWAY from the foundation.
Of course, by the nature of your question, I have to assume you live in a NON-ARRID part of the world. If you live in TEXAS, all bets are off.
BEE THE WATER> figure out where the water could be coming from... Do you have a sprinkler system that's leaking?
Does your neighbor have all of their water running onto your property?
Is your crawlspace ventilated properly? (LOTS OF VENTILATION IS GOOD!)
post back with more questions, we'll do our best to help...