Legionella Risk Assessment: Water Treatment

What water treatment methods can be used?

Cooling towers/systems are often treated using biocides. But there are other treatment strategies available such as ultra violet (UV) irradiation and ozone.

 

In hot and cold water systems legionella has traditionally been controlled by storing hot water above 60°C and distributing it at above 50°C - and keeping cold water below 20°C if possible. Other methods which are used when the correct temperatures can not be maintained include chlorine dioxide.

 

One way of controlling legionella is to keep water hot, which you may be using for other reasons already. For example, nursing homes and residential care homes tend to keep water hot for reasons other than controlling legionella, including kitchen and laundry use.

 

However, care is needed where water runs hot. The risks of scalding should be assessed and appropriate measures taken to prevent burns, eg warning notices and thermostatic mixing valves on taps.

Can water temperatures be reduced if using another method of controlling legionella?

IIt depends. If you don’t need the hot water for other reasons, then using another effective treatment method means that you can reduce water temperatures. There is specific advice on this issue for hospitals and you should refer to this. It recommends keeping the water hot and not reducing the temperature.

 

But whatever treatment method you use, you need to make sure you know:

 

• What the effective level of control is for your system, eg temperature and concentration of biocides
• If the treatment method can cope with changes in the system, eg variations in the amount of water used throughout the day.
• How you are going to measure the effectiveness of the treatment method; for example, if you are using temperature as a control method you can take the temperature of the water coming out of the taps.

Should samples be taken to test for legionella?

It depends. Sampling and testing for the presence of legionella bacteria is just one way of checking that your system is under control. But it is not a simple test - sampling and detecting legionella requires specialist help. Further details on how to sample and the frequency of sampling in both cooling towers and hot and cold water systems can be found in Part 2 of the ACOP and guidance.

 

 

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