Filter media retainer and underdrain system having a filter media retainer

A filter system for filtering a liquid containing particles, the filter system comprising:

• a) an underdrain block comprising a top wall, a bottom wall, and a pair of side walls extending between the top wall and the bottom wall to define an interior chamber, and
• b) a filter media retainer mountable on the top wall of the underdrain, the filter media retainer comprising:
• a plate having a first end wall, a second end wall, and a pair of longitudinal sidewalls connected to opposing sides of the first end wall and the second end wall, the plate having a top surface opposite a bottom surface;
• a plurality of hopper-shaped compartments on the top surface and having a first sloped wall and a second sloped wall angled toward the first sloped wall in a direction from the top surface toward the bottom surface;
• a top sidewall on the top surface of the plate separating adjacent hopper-shaped compartments from each other;
• at least one first slot extending through at least one of the first sloped wall and the second sloped wall;
• and
• at least one second slot extending through the top sidewall,
• wherein the at least one first slot and the at least one second slot are configured to allow a passage of filtered water in a direction from the top surface to the bottom surface, and allow a passage of a backwash fluid in a direction from the bottom surface to the top surface.