26 March 2021

Managing Legionella Bacteria in Hot & Cold Water Systems

Legionella Sampling & Analysis
Legionella Bacteria Sample - using culture method

Where conditions are right legionella bacteria can develop in both hot and cold water systems. Those responsible for facilities and building management have a legal obligation to control this risk through proper assessment, planning and prevention measures.

What Is Legionnaires’ Disease?

Legionnaires’ disease is a severe and sometimes fatal form of pneumonia, caused by the bacterium Legionella Pneumophila. It’s not a disease you catch from other people, but by breathing in tiny droplets of contaminated water. The bacteria lives in water, thrives in temperatures between 20 degrees Celsius and 45 degrees Celsius and grows fast where stagnation is able to occur. The disease can be deadly for anyone, but it is particularly dangerous for those in high risk groups such as the elderly and those who are immune compromised. 

Legionella Risk Assessment

Those with the responsibility for managing buildings are required, under the Health and Safety at Work Act 1974, The Management of Health and Safety at Work Regulations and more specifically, the Control of Substances Hazardous to Health Regulations 2002 (COSHH), to take suitable precautions to have a risk assessment carried out and depending on the outcome of the assessment, must manage the hot and cold water systems in order to control the growth of the bacteria. 

A legionella risk assessment should include:

  • Management responsibilities, named competent person/s and duty holders amongst others responsible for the health of your system
  • Evaluation of the competence and training of key personnel
  • A description of your system
  • Any identified potential risk sources
  • Recommendation for means of preventing the risk or controls in place to control risks
  • Monitoring, inspection and maintenance procedures
  • Reference to records of the monitoring results and inspection and checks carried out
  • Arrangements to review the risk assessment.

As an employer, or a person in control of the premises, you are responsible to reduce the risks of exposure to legionella and must understand how to:

Depending on what the building is being used for and the level of risk to users/occupants identified by the risk assessment:

  • Controls need to be established and documented
  • Schematics of systems need to be created
  • Testing and inspection regimes established
  • The results of any inspections, checks or tests need to be kept for a minimum of five years.

Here are some of the practical things that need to be thought about when it comes to controlling legionella in hot and cold water systems:

Temperature control

Typically, Legionella growth is controlled in water systems through consistent temperature control.

  • Hot water storage cylinders should store water at 60°C or higher
  • Hot water should be distributed at 50°C 
  • Cold water should be stored and distributed below 20°C.
  • Hot water storage cylinder temperatures should be checked every month and cold water tank temperatures at least every six months
  • Sentinel outlets should be checked monthly for their distribution temperatures 

Stagnation control

Water stagnates when it stands unused for an extended period of time. This encourages the growth of legionella bacteria.  To prevent this it is recommended that the following are done:

  • Removal of dead legs and dead ends in-pipe work
  • Flushing of  infrequently used outlets on a weekly basis
  • Cleaning and descaling of shower heads and hoses every three months
  • Cold water storage tanks should be cleaned periodically and water should be drained from hot water cylinders to remove debris

Founded in 2001, SMS Environmental are one of the UK's largest providers of full water and air hygiene and treatment services, offering a broad range of water treatment, analytical and environmental services with an emphasis on Legionella Control. 

SMS supply services to over 700 customers throughout the UK in every public and private sector, including housing, education, leisure, healthcare, commercial, defence, prisons, blue light and infrastructure organisations. 

For more information on water hygiene services, please call 0800 138 21 21 or use the form below.

Further Advice on Legionella

The official code of practice for legionella control:

L8 ACOP Legionnaires’ disease: The control of Legionella bacteria in water systems

Guidelines for hotels, office buildings and larger premises:

HSG274 Part 2 Legionnaires’ disease: The control of Legionella bacteria in hot and cold water systems

Guidelines for care homes and similar:

Control of Legionella in hot and cold water systems in care services / settings using temperature





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