Reverse-osmosis (RO) water filtration system for TrueSteam humidifiers to remove dissolved solids and organic matter from water by passing it through membrane which separates and flushes minerals and impurities from water. Install this system upstream of steam humidifier's water inlet. It is recommended that RO system's filters be replaced at least once per year to ensure optimal humidifier performance. Water quality test kit is used to determine need for reverse-osmosis system. Steam humidifiers require pure water to prevent corrosion from chlorine, salt, and other chemicals.