Hot and cold water systems

Systems to supply hot and cold water services 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 1 minute at the outlets.

This page will help you understand how to control risks for different systems, depending on the size and type of building.

It also explains how you can use HSE’s guidance to control the risk of legionella in hot and cold water systems.

Understanding your water system

Before assessing the risks, you need to understand the type of water system and its operation. Simplified examples of different basic systems are provided in Legionnaires' disease - Technical guidance:

smaller hot and cold water systems – non or low storage systems
hot and cold water storage – gravity fed system
a pressurised mains-fed water system
hot water storage only
cold water storage only – mains pressure hot water system

You will also need to understand any constituent parts of your water system, such as:

a dead or blind end (a redundant length of pipe closed at one end, which water cannot flow through)
thermostatic mixer valves (TMVs) – these blend hot and cold water to reduce the temperature where there is a risk of scalding
sentinel outlets – the nearest and furthest outlets from hot and cold water cylinders and tanks
a dead leg – a pipe leading to an outlet which water flows through but the outlet is unused or rarely used

Larger buildings

For larger buildings, with more complex hot and cold water systems such as large hotels and hospitals, you should consider the guidance in Legionnaires' disease: Technical guidance. It covers the following topics:

hot and cold water system types and descriptions (substitution)
water system design and commissioning (water system design considerations, cold and hot water systems, expansion vessels and commissioning)
operation and inspection of hot and cold water systems (supply water, maintenance, frequency of inspection and monitoring)
water treatment and control programmes (temperature regime, biocide treatment, supplementary measures)
microbiological monitoring
cleaning and disinfection (thermal and chemical disinfection)
shared premises and residential accommodation (landlords’ duty) special considerations for healthcare and care homes (water safety groups and plans, monitoring for legionella, scalding, flushing)

Healthcare establishments

For healthcare establishments, such as hospitals or care homes, you need to consider the guidance in the approved code of practise Legionnaires' disease: Technical guidance.

There is also specific guidance for healthcare and care homes in Part 2 of Legionnaires' disease: Technical guidance.

This includes guidance on how susceptible individuals should be protected proportionately. For example, in an acute hospital setting where many susceptible patients are likely to be at risk of infection, all aspects of the guidance may need to be followed. In other settings where there may be less susceptible residents, for example care homes, a local risk assessment will help determine which aspects of the guidance are relevant.

You should also consider the following 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:

Further guidance for care settings is available in health and safety in care homes.

Smaller buildings

This information is for smaller buildings in a range of businesses and organisations, from community halls to care homes and university multi-storey accommodation blocks.

It includes smaller buildings with less complex hot and cold water systems, for example, residential accommodation and housing associations.

As an employer, or someone in control of premises, including landlords of residential accommodation, you have a responsibility to carry out the duties in Legionnaires disease: what you must do. Following the duties ensures the risk from exposure to legionella in your premises is properly controlled.

You must take a risk assessment and review it if there are significant changes, for example expansion of water system and changes in resident population. You will also need to consider the susceptibility of your staff including 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.

However, for full technical details on managing your duty, you should consider the guidance in Part 2 of Legionnaires' disease: Technical guidance.

Using temperature as your primary control

When 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.

Managing your duty where temperature is not used to control risk

When temperature is not used to control legionella risk there are several alternative methods given in the guidance in Part 2 of Legionnaires' disease: Technical guidance.

However, it is important to demonstrate that you are achieving effective control and that other measures including inspection, cleaning, monitoring and recording are carried out.

Where temperature is not used to control legionella risk there are several alternative methods given in the guidance. However, it is important to demonstrate that you are achieving effective control and that other measures including inspection, cleaning, monitoring and recording are undertaken.

Scalding

There is a risk of scalding where water comes out of taps at temperatures above 44°C. In some facilities, for example care homes, this especially applies to whole-body immersion in baths and showers of vulnerable patients who may not recognise high temperatures and respond quickly, such as:

the very young
elderly people
people with disabilities
or those with sensory loss

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, a thermostatic mixing valve (TMV) Type 3 must be fitted to prevent water being discharged at more than 44°C.

You can find more information on scalding and burning in health and social care.