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Current IssueSeptember 21, 2014
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Ask The Expert: Principles of softening
04/10/2003 
 
Question: Q: I am curious as to how water softeners work. I know you place salt in the tank and the system regenerates every day or two, but how does it really work? What actually takes place to keep the water softened? Any help would be appreciated. Thank you.

Tom Grotovsky
R. Berti & Son Contractors Inc.
Lockport, Ill.  

Answer: A: Softeners operate on the principles of ion exchange. The principal mechanism is carefully manufactured polymer resins that have certain properties of attraction on a molecular level depending upon the materials used in their construction. Cleaning of these resins in household softening is done using salt (sodium chloride or potassium chloride) as the regeneration solution, or regenerant. This loads the resin bead exchange sites with sodium (Na) or potassium (K) ions, while the chlorides and any contaminant ions that may have been on the bead are flushed away in the discharge water. Contaminants with a certain electronic charge, or valence, which determines their level of attraction to the resin bead are removed from the water in exchange for Na or K. Since different contaminants have different valences, however, the rules of attraction—the principle of selectivity—may vary, which means that certain constituents may have a greater or lesser affinity for removal by the ion exchange resin under varying water quality conditions. In certain cases, some contaminants can displace others on the resin bead and release a greater concentration of a contaminant in the product water than was in the original raw water. This is one of the reasons why ion exchange can be considered a science and why softeners are not simply appliances that can be plugged in and left without any followup attention, since some of those contaminants—such as arsenic, radium, etc.—can prove to be potential health risks above certain levels. Always consult a professional when you have questions about selecting or maintaining a water softener. Ways to make sure you're dealing with an experienced residential water treatment dealer include checking to see if they've earned a Certified Water Specialist (CWS) designation from the Water Quality Association (WQA) and whether they're using equipment that has earned the WQA Gold Seal or met ANSI/NSF standards. NSF International promotes several such marks for varying types of drinking water treatment units, including softeners, filters, and reverse osmosis, ultraviolet and distillation systems. You can find listings of certified products at both the WQA and NSF websites: www.wqa.org and www.nsf.org (The WQA site also lists certified professionals, i.e., those with CWS designations.)

Hope that helps.

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