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Ultraviolet Light

Ultraviolet light (UV) is an effective means of disinfecting water. Ultraviolet light disinfects water by striking a microorganism with a 254Å (nm) wavelength of electromagnetic radiation at a specified intensity. This action disrupts the DNA, preventing the microorganisms from reproducing and thus effectively killing it. Sunlight can disinfect water the same way.   UV disinfection system

NSF has UV devices divided into Class "A" and Class "B" UV systems that differ based on their ability to treat water for different levels of micro organisms. Pathogens are affected differently by varying dosage intensities of UV light.

The National Sanitation Foundation describes Standard 55 for "Class A" UV light disinfection systems as follows:

"Class A point-of-entry and point-of-use systems covered by this Standard are designed to inactivate and/or remove microorganisms, including bacteria, viruses, Cryptosporidium oocyst and Giardia cysts, from contaminated water. Systems covered by this standard are not intended for the treatment of water that has obvious contamination or intentional source such as raw sewage, nor are systems intended to convert wastewater to drinking water. The systems are intended to be installed on visually clear water."

NSF Standard 55 "Class B" UV systems are designed to operate at a minimum dosage and are intended to "reduce normally occurring non-pathogenic or nuisance microorganisms only." The "Class B" or similar non-rated UV systems are not intended for the disinfection of "microbiologically unsafe water."

Transmitted UV light dosage is affected by water clarity. Water treatment devices are dependent on the quality of the raw water. When turbidity is 5 NTU or greater and/or total suspended solids are greater than 10 ppm, pre-filtration of the water is highly recommended.

See the Ohio Department of Health's Fact Sheet on Ultraviolet Light for Continuous Disinfection for more detailed information on ultraviolet light continuous disinfection systems.

Ohio Department of Health's Fact Sheet on Ultraviolet Light for Continuous Disinfection 

National Sanitation Foundation (NSF)

Page reviewed 12/09/2015