How Do I Know How Deep My Water Table Is?
The only way to really know is to dig a hole in the ground. If you want an approximate depth you can contact the Department of Water Resources in your area. They can get a well survey done for you. If wells are common in your area you can ask a neighbor how deep is their well. These methods will get you close because there can be a lot of variation over short distances depending on the sub-surface stratigraphy.