A French drain is simply a small trench, dug to a gradient that will allow surface water, or the top of the ground, to drain away from a building or area that is prone to surface water build up and/or flooding. The usual reason for constructing a French drain is to relieve a build up of water against a house wall or to relive a damp landscape area. We install perforated pipe and special fabrics to filter out the water from soil.