What Is a Water Table?

Part of the reason why crawl spaces are never fully waterproof unless they are encapsulated with a vapor barrier is because of how the water table can affect the space. Besides encapsulation, only an interior drainage system is capable of minimizing the damage a high water table can cause. Without draining out the water in the soil, there would be no way to stop moisture from seeping into the crawl space.  

• What It Is 

The soil in your yard may be dry, but a few feet down, the soil is saturated with groundwater. This is known as the zone of saturation, and it’s the area where groundwater perpetually resides. The water table is an invisible line that indicates where in the ground the zone of saturation begins. It starts just on the surface of all the groundwater. 

The water table is not a static line. It can rise and fall depending on how much groundwater is in the soil. In Charlotte, NC, the annual precipitation is about 15 inches more than the national average. It also doesn’t help that, because of the characteristics of the Cecil soil of the region, the topsoil is moderately well-drained, so all the rainwater easily seeps down into the subsoil. The rainwater accumulates underground, and the water table rises the more water accumulates in the zone of saturation.  

• How It Affects Your Crawl Space 

The depth of the water table is something that varies not just nationwide but also citywide too. Some properties have extremely shallow water tables while others have a water table an impressive few feet below ground. It’s not something that can be known unless you get a professional to evaluate your property. Still, there are many areas in Charlotte where the water table may not be so high, but because of the persistent summer rain in North Carolina, it rises considerably. 

When this happens, the water vapor from the moisture underground rises into the crawl space and raises the humidity levels of the space. The more water that is close to the soil during the winter will also contribute to frost heave, which is when the expanding ice puts upwards pressure on the crawl space posts and causes them to shift around. As a homeowner, you cannot control how much water seeps underground when it rains or snows, but you can control how much it gets drained out if you invest in a crawl space interior drain system.