Lightweight fibrous media (LFM) filter

An apparatus for filtering water, the apparatus comprising:

• an open mesh filter cartridge, and
• a perforated tube passing through an interior of the open mesh filter cartridge,
• wherein an annular space is formed between an inner surface of the open mesh filter cartridge and an outer surface of the perforated tube,
• wherein the open mesh filter cartridge includes a plurality of openings that permit unfiltered water to flow into the open mesh filter cartridge and into the annular space,
• wherein the perforated tube includes a plurality of openings that permit filtered water to flow into the perforated tube from the annular space located in the interior of the open mesh filter cartridge;
• and
• wherein the interior of the open mesh filter cartridge contains a plurality of compressed fibrous media balls each including a plurality of fibers extending outwardly therefrom, the compressed fibrous media balls, after being installed into the interior of the open mesh filter cartridge, remaining compressed within the interior of the open mesh filter cartridge, without a movable mechanical device providing a force onto the compressed fibrous media balls, by virtue of being positioned within the interior of the open mesh filter cartridge such that the fibers of the compressed fibrous media balls intermesh with each other and with the openings of the open mesh filter cartridge and with the openings of the perforated tube.