Reverse Osmosis Housing with 3 membranes. Housing 3250mm Long Diameter 6.5 Inches Each filter membrane measure 960mm X 160mm in diameter. 3 inch Input and Output with triclover fittings. Reverse osmosis removes contaminants from unfiltered water or feed water when pressure forces it through a semipermeable membrane. Water flows from the more concentrated side (more contaminants) of the RO membrane to the less concentrated side (fewer contaminants) to provide clean drinking water. The fresh water produced is called the permeate. The concentrated water left over is called the waste or brine. A semipermeable membrane has small pores that block contaminants but allow water molecules to flow through. In osmosis water becomes more concentrated as it passes through the membrane to obtain equilibrium on both sides. Reverse osmosis however blocks contaminants from entering the less concentrated side of the membrane. For example when pressure is applied to a volume of saltwater during reverse osmosis the salt is left behind and only clean water flows through.