Rainwater Filtration Joint for Concrete Surfaces. As a Sustainable Drainage System, the d-Rain Joint is a simple, low-cost, and robust onsite stormwater management alternative compared to other permeable, pervious surface options. The d-Rain Joint device directs the surface rainwater to an installed drainage bed beneath the impervious, “hardscape” surface. Using low-cost, harder substrate, the solution to provide a permeable, pavement system can be used wherever stormwater management requirements are needed for a driveway, parking lot, garage, large patio, community common areas and streets, pool areas, sports architecture, shopping or theme park developments, alleyways or public walkways.