... quartz sand filter, activated carbon (AC) filter and polypropylene fiber (PP) filter. As to high hardness of the raw water, the water treatment ... the osmotic pressure of raw water, water molecules can go through the RO semipermeable membrane, produce pure water, however, a large amount ... choose two stages reverse osmosis purification system, two stages RO pure water conductivity is about 1 ~ 5 u S/cm, ...