Controlling Legionella in Hot & Cold Water Systems

Controlling Legionella in Hot & Cold Water Systems Legionella bacteria exists naturally in many water sources. However, numbers are small in nature, and the biggest danger to humans tends to come from man-made water systems that are inadequately maintained or managed. Controlling Legionella bacteria in hot and cold water systems, cooling towers and other water systems is essential if you are to ensure the safety of people in and around your workplace is protected.

At what temperature will legionella grow?

Legionella bacteria will multiply in the water if temperatures reach 20 degrees Celsius and climb to somewhere between that and 45 degrees Celsius. Colder temperatures mean the bacteria fall dormant. Anything higher than 60 degrees Celsius will kill them.

Which water systems are at risk of legionella contamination?

Any man-made water system is potentially at risk. Here are some examples:

Hot and cold water outlets
Cooling towers
Spas and hot tubs
Decorative fountains and water features
Industrial processes that use water

These are just a few examples; there are many more. Every business that has hot and/or cold water outlets must perform a risk assessment to determine the level of risk present in this area. For some businesses, there will be no real risk at all, but other businesses – such as those in the healthcare sector, for example – will need to introduce special measures to reduce the risks as much as possible.

Controlling legionella in water systems using thermal disinfection

One of the main control measures for legionella bacteria in water is temperature or thermal disinfection. This means ensuring the water temperatures are outside the range identified for the proliferation of legionella bacteria. If hot water is stored, it should be stored above 60 degrees Celsius. Similarly, cold water should be stored below 20 degrees Celsius.

As a general rule of thumb you should remember the following:

Keep hot water hot
Keep cold water cold
Keep the water moving

Since scalding is a real danger in healthcare settings, particularly where vulnerable patients and residents are concerned, thermostatic mixing valves (TMVs) should be fitted. These will ensure the water temperature is high enough to kill legionella bacteria, but low enough to reduce or eradicate any risk of scalding from very hot water or burning from hot surfaces.

Dealing with stagnant water, little-used outlets and dead legs

Legionella bacteria will multiply more readily in stagnant water. Thus, unused or little-used outlets and pipes should be flushed regularly, or better still removed where possible. Dead legs or dead-ends in any pipework installations should be removed. Additionally, sentinel outlets at the nearest and furthest points from every water tank or similar receptacle should be checked for temperatures monthly. This applies to hot water tanks too, while cold water storage tanks should be checked a minimum of every six months.

Employing a legionella competent person

Even when a good legionella risk assessment is completed, proper control of legionella in all water systems will only be as good as the person who takes responsibility for this and the on-going management and control processes. A competent person is someone who is experienced and is trained in such work, who will regularly check and inspect the water system(s) and control measures put in place for issues. Regular cleaning is also a key part of this task.

Further information, advice and support

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