We all know that water runs down hill, with that being said crawl spaces are generally lower than the ground around the home because we backfill the foundation so that water shed will run away from the home. Over the years the backfill settles to a negative grade and allows water to rest against the foundation of the home. So when it rains hard in the spring and fall the ground becomes saturated. Once the ground will not take on anymore water it begins to run to the lower lying areas like ditches, storm drains and crawl spaces. Once standing water is introduced into the crawl space the homeowner runs the risk of major foundation failure and joist and beam rot. The major reason the standing water can be so devastating is because it goes unnoticed for long periods of time. The homeowner may periodically look in the crawl space for water or the source of an odor and not see any water. That does not mean in the last six months while the crawl space went un-inspected water did not come and go several times. Keep in mind the conditions described in the last paragraph and now add scum and rodent feces floating on top of the water inside the crawl space. It becomes extremely hard to reason that the old way of maintaining a crawl space is working just fine.