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Current IssueApril 17, 2014
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Ask The Expert: Ultraviolet `sterilizer`
06/08/2001 
 
Question: I would like to know if I can connect a UV system to my existing home water system (I am on a drilled well) in the country. We are presently in Ottawa, Ontario, but will be moving to Sussex, New Brunswick. We have already bought a house with a well and septic system. The well produces 7 to 9 gallons per minute on demand. Would a UV system be able to purify all of the water coming from the pump so we could be assured of bacteria/virus free water throughout the house, at every source. If so, could you recommend a system for me or a company that I may contact for additional information. I am looking for independent review information on UV water systems. Do they do what the brochures state? Glenn Wood
Sussex, N.B., Canada
 

Answer: You can apply UV to your house to disinfect the water, with the following constraints. UV disinfection is a physical process, which affects only those microbes directly irradiated by the UV lamp. Therefore, while you can install a point of entry unit which will provide effective disinfection to all water entering the house, that unit won't have any impact on those microbes which already live in the plumbing of your home, downstream of the UV lamp. For disinfection of water at the tap, you might want to consider a point-of-use unit, especially at faucets from which the majority of your drinking water is drawn. This might be more economical than treating all the water used in the house.

The claims made by manufacturers are certainly subject to scrutiny, so look for units which have been tested and certified against NSF Standard 55. This certification indicates that an independent testing facility has found that the UV system provides satisfactory bacterial disinfection. The requirements are more strict for point-of-entry than for point-of-use units.

As you also want to address viruses, be aware that these microbes are more resistant to UV than bacteria, so a higher UV dose must be delivered. To do so, select a UV system designed for 2 to 3 times the peak flow rate of your home water use. For you, this would be 15 to 30 gpm. Such a unit would have proportionately more lamp wattage, so verify that it's designed to not overheat during extended periods when there's no flow into the house.

As you're on a drilled well, I'm assuming your water is quite clear. If it's turbid or cloudy, however, the UV light would be prevented from affecting the microbes, so a filter ahead of the UV unit would be needed. High alkalinity (hardness) in the groundwater could also be a problem by causing scaling of the quartz sleeves, located between the UV lamps and water. Therefore, you might also need a water softener. The UV unit would be placed downstream of this.

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