You need to understand two things about UV light:
- It has germicidal properties. That means it can protect you from harmful microbes in drinking water.
- It’s invisible! So you can’t rely on seeing the blue glow from your UV system’s lamp to know your water is safe to drink.
UV light is electromagnetic radiation, light just beyond the visible spectrum. That’s a very important point. Because it’s outside the visible light spectrum, UV light is invisible to the naked eye. You can’t see it!
The UV lamp glows blue. What does that mean?
At best, it means your UV lamp is receiving power and disinfecting your water. At worst, it means you’re relying on a UV lamp that is no longer producing enough UVC energy to properly disinfect your water. It depends on how long the lamp has been in operation.
With a UV lamp, electricity is passed through a tungsten filament causing it to heat up. The energy of this heat “excites” the mercury vapour* contained in the lamp which, in turn, gives off UV light. How long the UV lamp can disinfect water depends on the rate at which the mercury vapour is used up. For most UV lamps, the elapsed time is about 9000 hours, or one year of continuous use. After this time, you may very well still see the blue glow. Again, that’s more a sign that the lamp is still getting power and not an indication that your water is fully disinfected.
The countdown timer (available on many UV system models), will count down the useful life of your UV lamp, from 365 days when it is first installed. When it reaches zero and the alarm sounds, it is signaling that the lamp needs to be changed, even though you may see that familiar blue glow through the view port.
UV light disinfects
The UV lamp is a critical component of your UV system, as it’s specifically the UV-C light it produces that disinfects your water. As the water passes by the UV lamp, those UV-C rays are absorbed by any microorganisms in the water, altering their DNA, and making it impossible for them to reproduce or cause infection. So in this way, harmful microbes like E.coli, Giardia, Cryptosporidium, and many others are made harmless. Often this is referred to as inactivated, but rest assured inactivated is as good as dead!
Seeing Should Not Be Believing
There is an old adage that seeing is believing, which suggests you shouldn’t believe in something you can’t see. But when it comes to your UV system, you should believe in the disinfecting power of UV light even though you can’t see it! And you shouldn’t believe your water is properly disinfected just because you can see the blue glow of the lamp.
*Not to worry, only a very small amount of mercury is used, typically <10 mg, and it’s safely contained!