Pretreatment water filters are filtration devices installed at the beginning of a water purification system to remove large particles, sediments, chlorine, and other impurities from raw water. They serve as the first line of defense, protecting downstream equipment such as reverse osmosis (RO) membranes, deionization units, and ultrapure water systems from fouling, scaling, and damage. Common types include sediment filters, activated carbon filters, and multimedia filters, each targeting specific contaminants to improve water quality before advanced treatment.