
Originally Posted by
Andy CWS
UV systems are designated by the National Sanititation Foundation (NSF) to Standard 55 as either Class-A or Class-B. Class-A systems to additional measures to assure water quality by requiring certain features that assure water quality. These can include, flow restrictors (for contact time), light intensity monitors (bulb function) and water quality (turbidity/clarity) sensors. If one of these features fails or reveals water quality problems, a solenoid shuts the systems down preventing contaminated water from coming through.
Prior to this I've not heard of turbidity/clarity sensors on UV lights but I am not up on the latest UV lights. I've quit selling lights with intensity monitored sensors due to the sensor failing and the owner mistakenly thinks the lamp doesn't have to be replaced annually because there was no alarm.
A solenoid valve is an option, I am not aware of any UV light that has a solenoid valve as a standard part of the light. If a solenoid valve is used, it will shut off the water to the house past the UV light whenever the power to the house or light goes off. In case of fire, and on average IMO, that is not a good idea. And many solenoid valves have a manual override and the owner will set it to open/off and that negates the reason for it.
Another feature of all UVs that I'm aware of is a visible and/or audible lamp out alarm. All UVs are flow controlled internally or require an external flow control.

Originally Posted by
Andy CWS
Go to
www.nsf.org to look up the brands that certify at this level. These are tested to maintain 40mj/cm2 by the end of a year's time (9000 hours) and a wave length of around 254 nanometers..
There are many UV lights that are not certified because the manufacturer will not pay the very high charges but, IIRC, the US government controls all UV light manufacturers and sets the minimum intensity of 16mj/cm2, or at least those manufacturers manufacturing for the residential markets.

Originally Posted by
Andy CWS
Class-B systems don't normally have all of these features but may have some. However, they are not recommended for pathological waters due to their lack of fail safe devices. They are tested to maintain 16mj/cm2 at the end of the bulb suggested life of 9000 hours.
That "not recommended for pathological ...." is personal preference, the US government says that 16mj/cm2 is the minimum all lights must produce for bacteria control in potable water. It would not be allowed if it didn't do the job the light is intended to do. That level will protect against the most probable types of bacteria found in groundwater. I would suggest a 40mj/cm2 light without the certification and expensive options as long as the price difference is not a problem.

Originally Posted by
Andy CWS
B systems can be combined with other disinfection systems such as chlorination, ozonation or some chemical applications. These are normally cheaper. Andy Christensen, CWS-II
IMO any salesman suggesting duplication of disinfection equipment is simply wanting to increase the sale price or has little confidence in the ozone, chlorine or other disinfectant system s/he is selling.
It is very easy to determine if a UV light is doing the job, simply do an at home Coliform bacteria test or have a lab do one.
Gary Slusser
22 yrs in water treatment and well pumps, 13 yrs helping people on the 'net to help themselves.
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