Reverse osmosis technology is used to purify water, which is the most advanced and effective membrane separation technology in the world. It is to separate material that can not pass through the semipermeable membrane from water when its pressure is higher than solution’s osmotic pressure. The hole of RO membrane is so small that it can remove dissolved salt, colloid, suspended solid and micro organism etc. The system is of good water quality, low energy consumption, no pollution, simple technology and easy control.