At the basis of the reverse osmosis purification system, there are semi-permeable membranes. The semi-permeable pore structure on these membranes is larger than the molecular diameter of pure water and smaller than the molecular diameter of the dissolved substances in water. When high pressure water is given to the membrane, only pure water molecules and 1-3% of the solutions in the water can penetrate through the membrane pores. Thus, while the solutions in the water are kept at a minimum of 98% depending on their diameter, microorganisms such as suspended solid particles, bacteria and viruses are filtered.