[ejwsr]

R/O units, Reverse Osmosis are rather simple really. First, water enters the unit under pressure through a central core of some type. The outlet of this core is restricted so that the input remains under high pressure. The magic begins here as the central core is usually a micropore membrane that only allows water molecule or smaller sized substances to pass. The high pressure side is the reject, brine or concentrate, as contaminants can't pass through the membrane layers. The low pressure side is the accept or clean water.

The accept water can and should be further polished using resin filtration. There are many advantages to an RODI unit, but they are tempermental and should be specifically engineered for the process that they will feed. The membranes foul and input water pH, free chlorine and ammoniacs can accelerate the fouling.

While pure water is an admirable goal, there isn't really any such thing except in sterile production and packaging. Since water is a universal solvent anything that is water soluble will immediately contaminate your pure water. Gases, minerals and particulate matter will find its way into the water.

So the question really comes down to one of comfort level with the systems out there, as well as thinking about what the critical substances are that must come out or be significantly reduced.

Hope this helps a bit in understanding the process as well as it's limitations. The plant I work in has three separate RO/DI units, so the above is experiential information.