A Horizontal Subsurface FlowConstructedWetland is a large gravel and sand-filled channel that is planted with aquatic vegetation. As wastewater flows horizontally through the channel, the filtermaterial filters out particles and microorganisms degrade organics. The water level in a Horizontal Subsurface Flow Constructed Wetland is maintained at 5 to 15cm below the surface to ensure subsurface flow. The bed should be wide and shallow so that the flow path of the water is maximized. A wide inlet zone should be used to evenly distribute the flow. Pre-treatment is essential to prevent clogging and ensure efficient treatment.