Water and other liquids can be disinfected with UVC light. To choose a UVC system with the right capacity (lamp power), it is important to know the transmission value of the water or of the liquid.


Read how disinfection with UVC light works


The transmission value (also known as T10 value) indicates the percentage of UVC radiation that remains after it moved through 10mm of water. The higher the value, the less shadowing effects there are in the water and this reduces the required power for sufficient disinfection.


Indicative T10 Values

  • Demineralized water: 99%
  • Spring water: 96%
  • Tap water: 90%
  • Rainwater: 80 – 96%
  • Ditch water: 60 – 80%
  • Drain water 20 – 30% (in horticulture)


The lower the transmission value, the higher the UVC intensity must be to still disinfect properly.
The intensity of the UV release can be increased by:


  • reducing the waterflow,
  • reduce the distance between the UV lamp and the outer wall or,
  • installing more or more powerful UV lamps,
  • use prefiltering before the UV system.

Increase transmission value through filtering

A UVC disinfection system does not filter particles from the water flow. To increase the transmission value, a pre-filter can be installed. Using a pre-filter can also prevent damage to the UVC installation and reduces the risk of deposits forming on the quartz tubes. For UVC installations in drinking water, 5-25 μm filters are commonly used.


Without pre-filtering, bacteria can end up in the shade of larger particles. If this happens, they are not illuminated by the UVC light and can simply continue on their way. By pre-filtering, the large particles are collected and shadowing is prevented.

View UVC water disinfection equipment