The key component of Reverse Osmosis water purification system, usually used in the 4th stage. It have very tiny holes, which allow only water and a few gases to pass through under certain pressure thus produce virtually pure water. The technology has been used in spaceships to recycle water for astronauts. It is effective in reducing hardness, heavy metals, toxins, free chlorine, bad taste, odor THM, Organics, hazardouschemicals and pesticides. Depending on inlet water quality or flow rate, it needs to be replaced every 24 months or 36,000 Gal. of water.