Furthermore, the Ultra-filtration using lifelike semi-permeable membrane and reverse osmosis methods becoming available enabled separation of colloids and ions from water.

[Fig.1] Shows the principle of reverse osmosis.

When pure water and salt water placed in a tank divided with a semi-permeable membrane (a membrane with extremely fine size holes on the surface), the pure water permeates the membrane and enters the salt water side of the tank, diluting the salt water. This is called Osmosis. The energy for this is called Osmotic Pressure, and depends on the concentration of the salt water. If the diameter of the membrane's holes is larger than the diameter of the salt molecules, the salt will migrate to the pure water side until both tanks are of the equal concentration level. This would be called Divergence.

As shown in [Fig.1] above, pressurizing the salt water using a membrane with very fine holes, only the water of the salt water solution migrates to the water side. This is called Reverse Osmosis. In actual application, a tubular formed semi-permeable membrane (for improved pressure resistance) is used. Filtered water and concentrated water are obtained when precision filtered water is pump pressurized and sent through the tube.

[Fig.3] shows a water purification system with a reverse osmosis module integrated