Government of Nova Scotia Government of Nova Scotia Nova Scotia, Canada


Drinking Water

Ultraviolet Disinfection For Drinking Water

Why would I need to disinfect my water?

Drinking water supplies are susceptible to bacterial contamination. Disease-causing organisms, known as pathogens, can be deposited in water by insects, birds, animals and people through various activities and weather conditions.

Disinfection helps prevent pathogens from causing illness. It is especially important when a water supply cannot be fully secured or protected.

Surface water is more susceptible to contamination than groundwater. Therefore, a properly constructed well is the first line of defence against contamination.

The next line of defence is in the home. Current research shows that when properly applied, ultraviolet (UV) light is an effective method of disinfecting water in the home.

I´ve heard of chlorination but can UV disinfect drinking water?

Chlorine kills disease-causing organisms. UV light renders them harmless by scrambling its DNA with radiation. The organisms become unable to reproduce and no longer capable of infecting a host (i.e., a human body) when consumed.

What should I know about the installation of a UV system?

Sometimes water can be contaminated in the piping system. Therefore, choosing the right location for a UV treatment unit is important. It should be installed in the home in a location to treat all water that is used for human consumption.

The unit is dependent upon an electrical supply. It is recommended that there be a circuit used solely for the unit. A UV disinfection system will not operate during a power failure unless there is a backup electrical supply.

To work, the UV light must reach the organism in the water. Anything that blocks the light may lessen its effectiveness. Therefore, particles should be filtered from the water before it passes through the UV treatment unit.

For UV disinfection to be effective, the water quality should meet the minimum limits as set by the manufacturer or the following parameters:

Water Quality Parameters
Parameter Limit
hardness: less than 120 mg/L
iron: less than 0.3 mg/L
hydrogen sulphide: less than 0.05 mg/L
manganese: less than 0.05 mg/L
tannins: less than 0.1 mg/L
total suspended solids: less than 5.0 mg/L
turbidity: less than 1.0 NTU
UV transmittance: more than 75 %

How do I know if my UV system is protecting my drinking water supply?

Once a UV system has been installed and is operating, check to make sure it is doing its job.

Most units have an indicator light to display that the system is turned on. It should also have a meter to show how well the light is transmitting. Check these visual indicators regularly to ensure the system is functioning properly.

You can´t look at a glass of water and see if the quality is good. Therefore, it is important to have the water tested to determine how well your water is being disinfected. It is recommended that the water being disinfected with a UV system be tested for bacteria once every three months.

Will UV disinfection always work?

By following the manufacturer´s requirements and these points, a UV system can provide effective disinfection of your water.

  • Use the best source water available.
  • If necessary, pre-treat water prior to UV disinfection.
  • Ensure the UV unit is designed for drinking water. The unit should indicate that it meets the NSF Standard #55 (Class A).
  • Install the UV disinfection unit as recommended by the manufacturer.
  • The light-monitoring device in the unit will indicate when the UV bulb needs to be cleaned or replaced. Check it regularly.
  • Filter the water using a 10 micron or less particulate filter.
  • Clean the quartz sleeve around the UV bulb on a monthly basis. Cleaning will help ensure the light remains effective. If the light transmission is significantly reduced, clean the sleeve more often.
  • Keep a record of when the light was installed, replaced and/or cleaned.
  • Change the light either as recommended by the manufacturer or as required based on poor water quality or reduced light transmission.
  • Have your treated water tested regularly to ensure your UV unit is effective.
  • Develop a contingency plan, such as using boiled or bottled water, in the event that the unit fails to operate.

For further information on water disinfection options, please call Nova Scotia Environment at 1-877-9ENVIRO