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Current IssueSeptember 04, 2015
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Ask The Expert: Whole-house RO system with copper pipes

Will putting a whole-house reverse osmosis (RO) system on a house with copper pipe cause leaks?




Will putting a whole-house reverse osmosis (RO) system on a house with copper pipe cause leaks?


The simple answer to your question is yes. Copper plumbing that is exposed to RO water will cause pitting; however, the question begs for a more thorough explanation of whole-house RO. To begin with, when most people hear the term RO, they think of water that has had the mineral salts reduced by 99 percent. While this is good for life support water, this is not practical for domestic,whole-house, working water. It is good to keep in mind that the water for this type of application should have a finish TDS of 50-100 ppm.

The product water off the membrane should pass through a small column of calcite or equivalent product, or it can be treated with soda ash to neutralize the acidic nature of the water to a less corrosive state. Bear in mind that these products must meet the NSF standard for food service.

In addition to neutralizing the acid, calcite will add calcium carbonate to the water. If the water being treated by the RO still contains hardness, then an acid feed is generally needed to drop the pH to increase the solubility of the hardness. This will allow the membrane to reject high levels of hardness while preventing scaling. Therefore, passing the water through a softener to remove any remaining hardness is a very efficient way to provide the kind of working water that most homeowners would like in the first place.

Gary Battenberg, Technical Director, Hague Quality Water International

As a rule of thumb, if the TDS (total dissolved solids) concentration of the RO water is above 10 ppm (almost all is >10), it should not be aggressive enough to dissolve copper and cause leaks.

Peter S. Cartwright, PE, Cartwright Consulting Co.

Whole-house RO units are, in fact, getting some serious play recently, due to the number of homes being built in areas that do not have a water source. These facilities typically drill their own well where often there are significant water quality issues that need to be addressed.

As a side note, keep in mind that depending on the design of the whole-house storage system,it is good to have a UV and a simple sediment filter after the holding tank before the water enters the house distribution system.

Shannon Murphy, Watts Premier, Inc.

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