Hot and cold water systems
There are various systems available to supply hot and cold water services that range in size, scale and complexity. All can present foreseeable risk of exposure to legionella. Temperature control is the traditional strategy for reducing the risk of legionella in hot and cold water systems. Cold water systems should be maintained, where possible, at a temperature below 20°C. Hot water should be stored at least at 60°C and distributed so that it reaches a temperature of 50°C (55°C in healthcare premises) within one minute at the outlets.
Before assessing the risks associated with these systems, you need to understand the type of system, its constituent parts and operation. Simplified examples of different basic systems are:
- Smaller hot and cold water systems – non or low storage systems
- Hot and cold water storage – gravity fed system
- Pressurised mains-fed water system
- Hot water storage only
- Cold water storage only – mains pressure hot water system
This site will help you to understand what you must do for
For larger buildings with more complex hot and cold water systems such as large hotels, healthcare establishments eg NHS premises, hospitals, you should consider the guidance in HSG274 Part 2 Legionnaires' disease: The control of Legionella bacteria in hot and cold water systems which covers the following topics:
- Hot and cold water system types and descriptions (paras 2.9 – 2.28)
- Water system design and commissioning (paras 2.29 – 2.56)
- Water system design considerations
- Cold water systems
- Hot water systems
- Expansion vessels
- Operation and inspection of hot and cold water systems
- Supply water
- Cold water systems
- Hot water systems
- Checklist for frequency of inspection and monitoring of hot and cold water systems
- Water treatment and control programmes (paras 2.80 – 2.118)
- Temperature regime
- Biocide treatment
- Chlorine dioxide
- Copper and silver ionisation
- Silver stabilised hydrogen peroxide
- Supplementary measures
- Point of Use filters
- Ozone and UV treatment
- Microbiological monitoring (paras 2.119 – 2.125)
- Microbiological monitoring
- Monitoring for Legionella
- Cleaning and disinfection (paras 2.126 – 2.137)
- Thermal disinfection
- Chemical disinfection
- Shared premises and Residential accommodation: Landlords (paras 2.138 – 2.151)
- Managing the duty – Residential accommodation: Landlords
- Shared commercial premises
- Special considerations for healthcare and care homes (paras 2.152 – 2.168)
- Healthcare and care home considerations
- Water Safety Groups and Water Safety Plans
- Monitoring for legionella
Health care establishments
In addition to considering information in L8 ACOP Legionnaires' disease: The control of Legionella bacteria in water systems and HSG274 Part 2 Legionnaires' disease: The control of Legionella bacteria in hot and cold water systems , you will also need to consider the relevant guidance from Department of Health (Water systems: HTM 04-01: The control of Legionella, hygiene, 'safe' hot water, cold water and drinking water systems) and Health Facilities Scotland (Scottish Health Technical Memorandum 04-01). This gives comprehensive advice and guidance about the legal requirements, design applications, maintenance and operation of hot and cold water supply, storage and distribution systems in all types of healthcare premises including hospitals and NHS Trusts.
HSG274 Part 2 provides specific guidance for healthcare and care homes where there are susceptible individuals but should be applied proportionately eg in an acute hospital setting where there are likely to be a large number of susceptible patients at risk of infection, all aspects of the guidance may need to be followed. However, in other settings where there may be less susceptible residents eg care homes; a local risk assessment will help determine which aspects of the guidance are relevant. Further guidance for care settings is available in HSG220 'Health and safety in care homes'.
For smaller buildings with less complex hot and cold water systems (eg residential accommodation, housing associations).
This information is for a wide range of businesses and organisations from community halls to care homes to university multi-storey accommodation blocks. As an employer, or someone in control of premises, including landlords of residential accommodation, you have a responsibility to undertake the duties in 'what you must do' to ensure that the risk from exposure to Legionella in your premises is properly controlled. You must undertake a risk assessment and review it if there are significant changes eg expansion of water system, changes in resident population. You will also need to consider the susceptibility of your staff and, particularly those more at risk of infection due to age, illness, infirmity, smokers, alcoholics or a weakened immune system.
In most cases, a simple risk assessment may show that the risks are low and are being properly managed and no further action may be required. HSG274 Part 2 Legionnaires' disease: The control of Legionella bacteria in hot and cold water systems (paras 2.138 – 22.146) gives further guidance on how to manage your duty. Where you are using temperature as your primary control, the following basic information may help you to understand the risks that your water system might present and the action you may need to take to help you make informed management decisions (Hot and cold water systems table). For those wanting full technical details you should consider the guidance in HSG274 Part 2 Legionnaires' disease: The control of Legionella bacteria in hot and cold water systems. Where temperature is not used to control Legionella risk there are several alternative methods (HSG274 Part 2 paras 2.80 – 2.118). However, it is important to demonstrate that you are achieving effective control and that other measures including inspection, cleaning, monitoring and recording are undertaken.
Where temperature is not used to control Legionella risk there are several alternative methods (part 2 section 168). However, it is important to demonstrate that you are achieving effective control and that other measures including inspection, cleaning, monitoring and recording are undertaken.
There is a risk of scalding where water comes out of taps at temperatures above 44°C. In certain facilities eg care homes, this is especially so for whole-body immersion in baths and showers of vulnerable patients, the very young, elderly people, and people with disabilities or those with sensory loss who may not be able to recognise high temperatures and respond quickly.
You have a legal duty to assess the risk of scalding and to adopt appropriate measures to control it. Your approach will depend on the needs and capabilities of patients or residents. For most people, the scalding risk is minimal where water is delivered up to 50°C at hand-wash basins and a hot water warning notice may be sufficient. However, where vulnerable people can get access to baths or showers and the scalding risk is considered significant, the fitting of thermostatic mixing valve (TMV) Type 3 is required to prevent water being discharged at more than 44°C.