A filter system for filtering water and/or wastewater including a sludge blanket clarifier for removing at least some impurities from influent. The sludge blanket clarifier includes a clarifier compartment in which a sludge blanket is to be formed to remove at least some impurities from influent directed into the clarifier compartment and through the sludge blanket. The clarifier compartment has at least one vertical sidewall extending from a bottom of the clarifier compartment to a top of the clarifier compartment. The clarifier compartment has a cross-sectional area that varies over at least a portion of a height of the clarifier compartment such that the velocity of influent just prior to entry into the sludge blanket is less than the velocity of influent just after entering the clarifier compartment.