Every once in a while we find ourselves faced with a water quality question whose answer we thing we ought to know, but for some reason never had cause to seek out in the past. A reader named ‘Nikelhoss’ recently asked,
“Which part of the nsf ansi standard 55 for ultraviolet water treatment systems applies to home units? Much thanks and thanks for the site, useful stuff on here.”
My friends, flattery may not get you everywhere, as the old saying claims, but it will make us blush. Plus we may answer your question faster. Ha ha. 😛
Rather than bore you by quoting the official definition of NSF/ANSI Standard 55 for Ultraviolet Microbiological Water Treatment Systems, we would like to point out a simple, yet often overlooked, truth that many people forget when exploring the wide world of water treatment systems for their home or business: Not every system will work for every water quality situation… and then we will provide a very relevant example to illustrate our point.
But first, let us preface this by saying NSF/ANSI Standard 55 applies only to point-of-use (POU) and point-of-entry (POE) ultraviolet systems not intended for use on public water supplies (i.e. in water treatment facilities).
- Class A — These ultraviolet water treatment systems must have an ‘intensity & saturation’ rating of at least 40,000 uwsec/cm2 and possess designs that will allow them to disinfect and/or remove microorganisms from contaminated water. Affected contaminants should include bacteria and viruses and the devices should perform in a manner that reduces threats posed by affected to a safe level.
- Class B — These ultraviolet water treatment systems must have an ‘intensity & saturation’ rating of at least 16,000 uw-sec/cm2 and possess designs that will allow them to provide supplemental bactericidal treatment of water already deemed ‘safe’ by an official (i.e. State or Local) health agency.
So… Which type (class) of ultraviolet water treatment system makes the most sense for home use? That all depends on the source water for the home. If the home has well water and uses no other disinfection method or draws its water from bodies of surface water, we think investing in an NSF/ANSI Standard 55 Class A ultraviolet water treatment system may work out best.
If, on the other hand, you live in town and have municipal water or use a reverse osmosis system with a large holding tank, we think an NSF/ANSI Standard 55 Class A ultraviolet water treatment system may work out best — though, as always, we suggest testing your tap water for a period of time to establish a water quality baseline (to make certain more sinister bacterial contamination issues do not exist) before investing in a water treatment system designed to serve as a backup disinfection device.
For the purpose of putting a final UV polishing on drinking water previously determined ‘safe’, a device such as those listed on the Water Quality Association’s Gold Seal Certified Class B Disinfection Ultraviolet Water Treatment Systems may work out best, though one could easily still use a Class A unit in a Class B unit’s place — but not the other way around!