A water treatment system for a water reservoir comprises a collection box； a rotary drum filter arranged to receive gravity flow from the collection box through a receiving line； a primary bio-filter； a secondary bio-filter； one or more connecting lines originating at the rotary drum filter and comprising at least a first outlet line connected to the primary bio-filter and a second outlet line connected to the secondary bio-filter, the second outlet line comprising a pump； and a return line originating at the primary bio-filter and terminating at the water reservoir. The collection box has a bottom and sides defining an interior volume, and comprises a first water intake having a first riser； a second water intake having a second riser； and a third water intake having a third riser, each riser being disposed inside the interior volume and extend upwardly from the bottom of the collection box.
