Because the upward flow of air through an underdrain creates low-pressure zones in the underdrain, some orifices can become starved for flow . . . or even reverse flow. Leopold has designed a water recovery channel into its Type S® Technology Underdrain to help ensure uniform and continuous airflow from all of the top deck orifices. The water recovery channel is designed to allow water to re-enter the underdrain to equalize the low-pressure areas. This dramatically improves the performance of the underdrain and provides superior results, particularly with the dual lateral design.