Clarified water from the clarifier overflow channel is evenly distributed to the 4 gravity dual media filters at the Filtration Basins through a 4-350 mm steel pipe where the remaining colloidal particles are being filtered at the filtration chambers, which utilized 2 layers of filter media, the Anthracite over the Silica Sand. The HDPE Type-S Underdrains with Filter Caps on top are installed underneath the filter media to serve as a means of collecting the filtered water, provide a means of backwashing the filter media and act as a barrier so that the filter media will not pass through the next stage.