Drainage pipes remove water when the groundwater level is higher than the position of the pipes. Water follows the path of least resistance and flows downward. For this, a hydraulic head difference is always required (the height difference between the groundwater level and the depth of the drainage pipe). The drain first removes the water that is closest to the pipe.

Water located further away from the pipe flows along flow paths to below the pipe. As a result, approximately two thirds of the water enters the drainage pipe from below. Due to the pressure from the higher groundwater level, the water is forced into the drainage pipe and discharged to the outlet pipe, which usually drains into a ditch.

Sandy and clay soils.