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Corrosivity of distilled water

I have a medical device that circulates temperature controlled water to provide therapy for various reasons. The device has a pressurized copper refrigeration coil in the water path to maintain bath temperature. I would like to know what type of water to recommend that the hospitals use in these systems.

I understand that DI water is corrosive and I believe that, over time, DI water would remove copper until the integrity of the coil was compromised enough to result in a refrigerant leak. Should I prohibit the use of DI? Would DI corrode the copper coil to failure in a relative short period?

I don't know much about distilled water, but, from what I have read, it is very similar to DI, it just uses a different method to remove impurities. Is distilled water as corrosive as DI?

I thought RO water was less pure than DI or distilled, but, I am not sure. How corrosive is RO?

Finally, with my limited knowledge concerning water systems, I would think that soft water would be the best option to balance the corrosivity issue with scale build-up.

I appreciate any help that you can provide.

Greg Willis
Quality analyst - Cincinnati, Ohio, USA
August 17, 2010

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August 19, 2010

Unfortunately, DI, Distilled and RO water are all fairly corrosive to copper if no corrosion inhibitors are added to the water.

If this is water with direct human contact, then softened water might be a good choice. However, any recirculated water without biocides, or UV disinfection can grow bacteria, legionella, etc.

If you don't have a chlorinated supply or are unwilling to change the water frequently, then your best course of action would be to contact a company that sells water treatment chemicals. There are many fine companies to choose from.

Lyle Kirman
consultant - Cleveland Heights, Ohio