Pre-Filter designed to fit the SteriPen ultraviolet light (UV) handheld water purifiers * Removes particulate from water with a 4x4-micron filter screen * Allows either pour through or immersion methods to filter the water * Clear, filtered water optimizes the ultraviolet purification process * Recipient of the Water Quality Association (WQA) Gold Seal, certifying that SteriPen purifies water safely and effectively