What is UV Transmittance & Why Is It Important for Water Treatment?

UV Transmittance, as it relates to water treatment, is the measurement of how easily UV wavelengths of light can pass through the water being treated. UV Technology has become a preferred way to disinfect water. Germicidal UV light is capable of destroying pathogens in water such as bacteria, viruses, and cysts like Cryptosporidium and Giardia. But in order for UV system to work properly, the water being treated must be able to transmit this light energy to the organisms being destroyed. Perfectly pure water has a UV Transmittance (UVT) value of 100% but water that has dissolved elements or organic materials will have a UVT value lower than 100%. This means that some of the UV energy is being absorbed by the water and less is available for disinfection. If the UVT value is too low, a situation can be created where there is insufficient UV light available to accomplish disinfection at all. Most UV manufacturers suggest that UV technology is only used where the UV Transmittance is at or above 75%. The vast majority of well water supplies are above this value. Surface water though can and often does have a UV Transmittance value below 75% due to the presence of UV-light-absorbing organics. In these situations tannin filtration is often a highly effective way to boost pH and make UV technology a viable option for disinfection. Carbon filters will also do a decent job though they tend to become exhausted quickly even when moderate concentrations of tannin are present.