To produce great quality water, any water filtration processes can be different at each of plants cause of the quality of incoming water.
The quality of the incoming water could be different because of:
      the types of activities
      natural minerals
      weather or season conditions
      natural resources

REVERSE OSMOSIS WATER TREATMENT
Reverse Osmosis is a process that is often described as filtration
Reverse osmosis (RO) is a membrane technology, but most well-known for its use in desalination for drinking water production. Reverse osmosis water treatment allows passage for only small and weakly charged molecules, such as water. Undissociated acids, such as carbonic acid (H2CO3), can also easily pass through. Carbonic acid is part of the carbonate system and not a contaminant—it affects the pH of the product water. Sodium and chlorine, which only carry a single charge and are also small, can pass through the membrane but not quite as easily as water. Molecules that are larger and/or more strongly charged than sodium and chlorine are rejected altogether.

Determining RO Membrane Performance
Rejection
     Salt rejection is the most important performance parameter. Membranes with higher salt rejection are categorized as “tight” membranes, higher rejection also require higher pressures to push water through the tighter membrane.
Temperature and pH
     Salt rejection is affected by water quality parameters, including temperature and pH. With increasing temperatures, the membrane diffusivity increases and both water and salts can pass through more easily. Fortunately, the increase in water passage is greater than the decrease in salt rejection. However, pH affects the scaling index of the raw water, and scaling can result in hydraulically irreversible membrane fouling and a loss in membrane water flux. Tight pH control can help prevent membrane fouling, which might otherwise lead to costly replacements of the RO membranes.
Free Chlorine
     Additionally, RO membranes can be susceptible to degradation from chlorine.

Online Monitoring for RO Systems
Conductivity Monitoring
     The membrane is a small barrier between raw water contaminants and a clean finished water. Real-time monitoring is crucial for keeping apprised of integrity issues with the membrane and the process as a whole.
Free Chlorine Monitoring
     Additional monitoring will ensure that your water is within the parameters acceptable for your membrane. Free chlorine monitoring before the membrane confirms complete dechlorination via sodium bisulfate and monitoring after the membrane ensures a sufficient chlorine residual.
ORP Monitoring
     Chlorine can also be monitored through measurement of the oxygen-reduction potential (ORP). This is a common technique in swimming pool monitoring. A high ORP reading indicates an oxidizing environment and alerts to the presence of oxidizing compounds, including chlorine, ozone, and hydrogen peroxide. A low ORP indicates a reducing environment, which may be a result of excess sodium bisulfate for dechlorination.
     In addition to conductivity and ORP monitoring, online monitoring of pH and temperature provide useful, if not crucial, information to confirm the raw water is within operational parameters.

DI or de-ionized water
     DI or de-ionized water is simply water that has had most of the mineral content and dissolved ion content removed. It is pure water. The cleanliness of the water is rated as its resistance value.

     DI water is classified into several types dependent on its use. If you are cleaning high end semiconductor final cleaning of optics or high end medical devices, then type 1 is the correct choice. Type II DI water is also used for high end cleaning and for food grade products. Type III is commonly used for parts cleaning and general lab ware cleaning. The charts below give the specifications for the various types of DI water.