What about a wiper on a UV light?
Some of you don't know what I am referring to when I say a "wiper on a UV bulb." OK, here is what a wiper does: It used to be that some ultraviolet lights (especially commercial ones) utilized a rod that had an seal or o-ring connected to it that you could slide the rod the length of the quartz sleeve and wipe it off. It sounds good in theory, but in reality the thinking behind it is somewhat flawed.
Here's why: Ultraviolet works by transferring light through the quartz sleeve through the water to neutralize (effectively killing) bacteria. Ultraviolet light typically works at 254 nanometers (wavelength) and it is critical that the water be as clean and clear as possible, so that the little critters don't have anyplace to hide. The wiper is supposed to keep the quartz sleeve clear of debris, however it usually doesn't.
If the water happens to be hard, the hardness itself can build up on the quartz sleeve and no wiper is going to remove that. If there is sediment in the water, it can settle on the quartz sleeve, but the fact that it is in the water is a huge red flag - the sediment serves as protection for the bacteria from the UV light. Even Ray Charles could see that isn't a good idea.
The same goes for iron, sulfur or manganese, bacterial slime and the like. If any of those are in the water, they should be removed first.
So, in reality, a wiper is a something that might make someone feel good, but doesn't really do much. The most important thing is pre-treatment. If the water is hard, it may need a water softener or conditioner or even polyphosphate to prevent the Ultraviolet bulb from being coated with the calcium and magnesium. Additionally, iron, slime and other solids in the water tend to obstruct the transference of UV light in the disinfection chamber.
Pre-treatment can include the following:
Wipers are like putting a band-aid on a gunshot wound - it's just not enough! If you are not sure what's in your water - have it tested