Everpure Pre Filters have been manufactured for those with very heavy water with high levels of impurities. Pre Filters are attached to water lines ahead of the standard primary water filter system. Pre Filters capture the larger particulates in the water, allowing the main water filter system to function more efficiently filtering the finer impurities. Shop Everpure Pre Filters and Replacement Cartridges at IceMachinesPlus.com. We have a price match guarantee plus expert customer service and competitive prices! Call 877-900-4423.