MRCOOL's water dispensers feature two different water filtration systems for higher water quality, reverse osmosis and ultrafiltration. Reverse osmosis (RO) filters using a semipermeable membrane. This membrane allows water to filter through but blocks larger molecules, like bacteria, minerals, salt, and nearly all dissolved substances. Reverse osmosis separates the molecules from one another and offers a higher degree of purity. Ultrafiltration (UF) uses a hollow fiber membrane. This membrane filters out solid debris and contaminants, like sediment and chlorine. Unlike a reverse osmosis system, ultrafiltration can allow minerals to remain in the water.