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  for Metal Finishing since 1989
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R/O vs DI water for finishing stainless steel

We currently are using DI water to finish our parts and are considering switching to R/O water because of the cost of new resin. We use around 60000 gallons per year. Could we see any negative affects from the R/O water verses DI water?

Scott McManaway
- Valencia, California, USA
2005

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Cost? Have you done a cost analysis? If so, it would be interesting to know your outcome. Otherwise, there should be no technical issues.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005

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An RO system will not make water quality as good as a DI system.

If you are using exchange tank bottles to make the DI water, putting an RO system in front of the exchange tanks will reduce the tank exchange frequency by more than 95%, without sacrificing water quality.

Lyle Kirman
consultant - Cleveland Heights, Ohio
2005

I have never heard of a RO system that could make 18Mohm water. That said, it will produce water that is very adequate for most plating systems. RO is expensive up front and requires some tender loving care of the membranes, but is rather cheap water after that. DI costs less up front, but regeneration costs can be high and that is forever.

James Watts
- Navarre, Florida
2005

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Whilst RO water probably cannot produce 18MOhm water, such purity would not normally be required for a conventional plating bath system. No matter how pure the water is when it is first produced, it will quickly deteriorate if not stored correctly. RO water often has a UV light installed in the circuit to prevent the build-up of bugs, and it is continuously recirculated to remove any contamination. DI water is not usually processed in this way as it is a cheaper basic installation and going on that route would not be beneficial if UV lights had to be installed. Furthermore, the purer the water, the better it is as a solvent and the more susceptible it is to collecting impurities and becoming contaminated. If you ant really pure water, you also have to consider the pipework quality and materials.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005