In the UK, Ultraviolet (UV) systems have been installed as part of a swimming pools filtration system since the 1994 and are highly recommended by PWTAG for commercial facilities.

They are used for secondary disinfection for protection against chlorine resistant bacteria such as Cryptosporidium and Giardia as well as the destruction of combined chlorine. These benefits have meant that UV is specified on all new commercial swimming pool installations.


Ultraviolet light is electromagnetic radiation of wavelength 100 to 400nm. Within this wavelength range, there are 4 sub bands of UV –

  • UV-A 315nm to 400nm
  • UV-B 280nm to 315nm
  • UV-C 200nm to 280nm
  • Vacuum UV 100-200nm

The UV light is produced when an electrical current is passed through a vacuum tube containing an inert gas and Mercury. This is essentially the basic construction of a UV lamp commonly used today.

As water passes through a UV system, it is exposed to UV light. Any microbes within the water are inactivated due to a disruption within the bonds in their DNA. This causes a mutation which stops the microbes from being able to reproduce or repair itself. UV light is effective against all known microbes, pathogens and spores however it is important to understand that each microbe has a different sensitivity to UV light and requires different levels of UV dose to be inactivated. Chemical compounds in the water are also affected and depending on the UV dose and wavelength can be broken down into harmless by-products.

For UV systems in swimming pool applications, we only recommend Medium Pressure UV and this is backed up by PWTAG guidelines. This is because Medium Pressure UV systems produce a polychromatic output of UV at wavelengths between 200 and 400nm. Therefore it produces an output suitable for microbial disinfection which is known as the germicidal range between 250 and 280nm but also a UV output above 280nm which is required for combined chlorine destruction.


  • Increased Bather Comfort – reduction in combined chlorine
  • Improved Health Benefit – protection against chlorine resistant bacteria
  • Crystal Clear Water – oxidising of organic material in pool water
  • Reduction in Corrosion – combined chlorine attacks stainless steel
  • Reduction in Chlorine Set Point – installing UV reduces reliance on chlorine
  • Easy to retrofit – due to recent innovations, UV system have much smaller footprints


Sterling has a large reference list of UV installations across the UK. We primarily work with trusted manufactures such as ATG Evoqua and Hanovia, who are at the forefront of advances in UV technology.