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Current IssueAugust 31, 2015
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Ask The Expert: RO & UV in Malta

Q: I have a couple of questions. Question 1—As a final polishing treatment of our undersink home RO unit we have always used silver impregnated carbon cartridges. UV treatment has been recommended for some time now. One sales rep stated that following long idle periods, the water will be hot for the first pint or so but then the temperature will return to normal. What worries me is the fact that, like most home systems, our system is generally used only in the mornings and in the evenings, with long hours of idle or no flow. Will these thermal shocks affect in any way the UV system components? And what are the pros and cons of UV treatment vs. silver impregnated carbon as a polishing treatment? Question 2—We need to obtain about 20 meters of quarter inch stainless steel tube in one length. Would you know of any suppliers? Thank you for great magazine.

Jimmy Sant



A: A UV system sitting idle for hours will increase water temp as heat from the lamp is absorbed by the water. Typically, the lamp may be as hot as about 50°C (assuming a low-pressure lamp). We can only suggest you check with the UV manufacturer to have them confirm that it would not overheat, and if overheated would it:

a) Cause premature lamp failure?

b) Cause gaskets or any plastic materials, etc., to become so hot that they may distort and allow water to leak?

c) If the RO unit is properly serviced (i.e., filter changes, etc.), you shouldn't require silver membranes downstream.

d) UV is a good choice over a membrane as it should require less servicing, and if sized properly will provide a barrier against waterborne pathogens. If the system is run frequently, you shouldn't have biological build up downstream of the RO as bacteria sized particles would be removed at that stage. However, UV is a good extra protective barrier downstream.

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