August 4, 2008 
This entry was posted on Monday, August 4th, 2008 at 8:16 pm and is filed under Ultraviolet Units. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
Ultraviolet (UV) radiation is higher in the electromagnetic spectrum than visible light. It is known to be effective in killing bacteria and pathogens. The only type of pathogens that cannot be killed by ultraviolet are those with hard coverings, such as giardia cysts. Ultraviolet purifiers are made for the specific purpose of disinfecting water and are not effective in removing other pollutants which requires that a high quality water filtration system also be used.
Most materials, including modern glass, do not transmit ultraviolet radiation efficiency. One of the best transmitters of UV radiation is quartz glass, so it is used for most UV lamps. In order for a UV unit to disinfect water effectively, three conditions must be met: (1) the UV lamp must produce radiation above a critical intensity; (2) the water must be subject to this radiation for a minimum period of time; and (3) both the input water and the UV unit itself must be clean. UV units employ many different designs to meet the first two conditions: one with water flowing straight through a quartz cylinder past a long tubular UV lamp and the other with the water conduit wound in a spiral to increase the amount of time the water is exposed to the UV lamp. In the latter design, the spiral tubing must also be of quartz glass in order to transmit UV energy efficiently.
To meet the the third condition, clean water, pre-filters must always be used. If the water contains particles, some bacteria and other pathogens will be shielded from the UV radiation and will pass through the unit unscathed. Because water cleanliness is so critical to UV operation, all UV units for home use need to be designed to allow easy access for cleaning.
UV treatment adds nothing to water and takes nothing away. The advantage of this is that no toxic disinfectant remains in the water, as it does with chlorine disinfection. But that’s also also a disadvantage: If pathogens enter the water at any point after the UV treatment, there is no residual disinfectant to kill them which is why you should use a UV treatment in conjunction with a standard water filtration unit.
Excerpted from “The Drinking Water Book, How to Eliminate Harmful Toxins from Your Drinking Water” by Colin Ingram.