A filter system employing a modular filter and at least one high rate pre-treatment system for expeditiously and effectively filtering water. The modular filter includes a reservoir housing for containing fluid. A plurality of filter cells are disposed in the reservoir housing for filtering influent passed through the reservoir housing. Each of the plurality of filter cells has at least one layer of media. A moveable backwash assembly is provided for sequentially backwashing the plurality of filter cells. The backwashing procedure is performed on the modular filter system such that while one of the plurality of cells is being backwashed the remaining cells are filtering pre-treated influent processed by the pre-treatment system. The pre-treatment system preferably has a footprint considerably smaller than the footprint of the modular filter. Further, the pre-treatment system preferably includes at least two pre-filters such that when one of the pre-filters is being cleaned the other pre-filter is still directing treated influent to the modular filter for further processing.