Recent research has shown that medium-pressure ultraviolet lights may be superior at eradicating recreational water illnesses.

The studies two published in Applied & Environmental Microbiology and one in Water Science and Technology: Water Supply showed that E. coli damaged by low-pressure UV can repair itself when exposed to light, a process known as photoreactivation. E. coli DNA exposed to medium-pressure UV under laboratory conditions showed little to no repair.

In addition, the deactivated bacteria may cause growth of new bacteria. According to a study by the Civil Engineering Department of the National University of Singapore, ?disinfection byproducts produced by UV disinfection ? may serve as a carbon source in finished water, resulting in regrowth of the bacteria.?

UV disinfection has become popular in indoor facilities to reduce chloramines and kill viruses and bacteria such as cryptosporidium, which takes nearly a week to kill with chlorine. However, the debate between low vs. medium-pressure UV has become heated as the issue of recreational water illnesses moves to the forefront of aquatic health. Many experts believe medium pressure, a more costly option, is better because of the possibility of photoreactivation. Others say that in aquatic environments, there?s no real difference between the two.

?Medium is better due to the possibility of photoreactivation,? said Tom Schaefer, national sales manager at Engineered Treatment Systems in Beaver Dam, Wis. ?But the reality is that for the pool, it?s a ridiculous argument to make. If you have bacteria and viruses in your water, and any residual chlorine, it?s going to disinfect that within seconds.?

Schaefer also argued that because photoreactivation requires light and UV systems are more prevalent in indoor pools where sunlight isn?t an issue, using low or medium pressure does not make a difference.