The original water (tap water, surface water, underground water) is sent to pretreatment system by adding pressure to be filtered roughly, the to be fitered by sophisticated filtered, and the water is transmitted to primary reverse osmosis by one-stage high pressure to be filtered, then the water is added pressure again.by sencondary high pressure pump and sent to sencond reverse osmosis system to produce the product water, this source added is called two-stage reverse osmosis. Raw water conductivity more than 500μs/cm, purified water conductivi- ty 1-10μs/cm.