Did you or a service provider try to get into your crawl space and end up finding a muddy pool?! You may have standing water in your crawl space without even knowing it. I can't count the number of times I've been told that a crawl space doesn't get standing water, then I crawl in after a rain and low and behold there is a small pond in there. Most of the time you can tell there has been standing water in a crawl space by just looking at the foundation walls. Just like if you were at the lake and the water was lower than normal, you could see the impact it has on the rocks and there is a clear line where the water usually is. This effect- called efflorescence- is where the water leaves behind salt deposits on the foundation walls. So where is this water coming from and what can you do to fix it? Essentially there could be many reasons, so let's try to tackle them all.
First and foremost, if you are in a high rain area like here in Western Kentucky, you need to be sure you have good, working, CLEAN gutters. Gutters are not for keeping the rain off your head as you come and go from your home. Without gutters, or without clean gutters, all the water from your roof is hammering the ground around your foundation. This will wear down the ground around your home, which initially was built up so that you have a slope away from your home. Debris-filled gutters or a lack of gutters entirely then leads to low areas for water to collect, right next to your foundation. That water will find areas to enter into your crawl space or basement from there. Let's say you do have clean, well-functioning gutters and yet, even that isn't cutting it and you have found water is entering your crawlspace. You need to redirect the water leaving your gutters away from your home. To give you an idea of how much water we are talking about: say you have a 1,500sqft home and it rains just 1 inch, that is going to be roughly 1,000 gallons of water. That is a lot of water potentially pouring into your crawlspace! In my personal experience, poor gutter drainage is the leading cause of water in the crawl space or basement. Again however, this may not be the only contributing factor to the small pond growing under your home.
The next thing I would check for is how the house is sitting within its surroundings. Is there any part of the yard sloping back towards the house? Is there a hill on one side? Or is it in the middle of flat land? These can all lead to water entering the crawl space or basement. If you do not have sufficient slope away from your house then you may want to look into running a curtain french drain around your home. This will help take the water that is running towards your home and redirect it to a more desirable place away from the foundation.
If you have good gutter and yard drainage but water is still entering your crawl space or basement, then you may have a high water table in your area -especially if your home is on a flat piece of land. The water just has nowhere to go since the ground is already so saturated. You could also have an issue with hydrostatic pressure. What's that? Basically the soil outside your foundation that is saturated with water creates pressure that will push against your foundation walls and can crack or split some blocks, giving an avenue for water to enter under the home.
Lastly, you may have to look into the option of a sump pump. It is my belief that sump pumps should be a last resort, but sometimes it is the only thing you can do. If all gutter and yard drainage issues have been properly remedied and you still have water entering your crawl space, then a sump pump should be installed. If you jump straight to a sump pump without addressing your drainage issues then you are still allowing water to enter your crawl space or basement, which will lead to moisture in the air, and could lead to mold and other high cost repairs.
No foundation is perfect, if you give water a chance to enter, it will. So do what you can to keep water away from the foundation and your chances of having standing water under your home will diminish greatly. As a last resort install a sump pump, but make sure it drains far enough away from the foundation. Lastly, make sure you have a quality vapor barrier installed to keep your moisture levels down.