Reverse Osmosis System Basics

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Reverse Osmosis and De-Ionization Demystified

Reverse Osmosis systems purify water by passing it through a series of filters to remove large contaminants and harmful chemicals/pollutants and then by forcing it through a special plastic membrane to remove very small contaminants. In the filtration stage, tap or well water first passes through sediment filters where silt, sediment and particles (like sand and clay) are removed. Water is then forced through a high efficiency carbon block filter where micro-pulverized carbon efficiently adsorbs chlorine, chloramines, pesticides and other harmful organic chemicals and pollutants. The pre-filtered water, now stripped of membrane-damaging particles and chemicals, flows into the RO membrane module where pure water molecules are forced through the RO membrane leaving salts, metals, bacteria, viruses, pyrogens and other impurities to be flushed from the system.

How De-ionization Works

Reverse Osmosis membranes, although very good at removing contaminants, still allow trace amounts to pass through. Nitrates, phosphates and silica are among these substances not fully removed. By further processing RO water through multi-layered, mixed-bed de-ionization cartridges, even those difficult to remove chemicals are reduced to virtually undetectable levels. The De-ionization cartridge contains resin beds of positive ions (cations) and negative ions (anions) which react with contaminants to chemically remove them from the water stream. The result is ultra-pure water that is extremely low in contaminants.

Some common stages used in RO/DI filters

  • Sediment filters
  • macrofiltration and sediment removal (dirt)
  • Active carbon
  • Removes Chloride, color, taste
  • Osmoses membrane
  • Filters out molecules like ammonia, nitrite, nitrate and countless other items that might still be in the water.
  • De-Ionizer
  • Charge molecules

RO/DI filters come in many different configurations. Some are 3 stages, some are 4 stages, and some are 5 stage. I believe I have seen filters with more than 5 stages but I do not feel they merit the extra cost. The additional stages are usually composed of additional carbon or sediment filters of different sizes. You can get just an RO filter or just a DI filter. Make sure you know what your buying as a DI filter will do nothing in the way of removing the pollutants that’s in your water.

On a final note remember to maintain your RO/DI filter. Follow the manufactures suggested replacement schedule when it comes to the filter cartages. A “dirty” filter is not going to give you any benefit by using it.

Should you have any questions or comments about this article please feel free to post in the Saltwater & Reef – General Discussion forum.

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