Updated: 22 August 2026
Introduction
Controlling water temperature is one of the most important ways of reducing the risk of Legionella bacteria within hot and cold water systems.
Legionella can multiply when conditions within a water system are favourable, particularly where water is allowed to stagnate or remain within a temperature range that supports bacterial growth.
So, what temperature kills Legionella — and what temperatures should UK businesses and building operators maintain?
This guide explains the key temperature limits and the practical requirements used for Legionella control in the UK.
🌡️ What Temperature Kills Legionella?
Legionella bacteria are particularly sensitive to higher water temperatures.
According to Health and Safety Executive (HSE) guidance:
- Below 20°C – Legionella can survive but generally does not multiply.
- 20°C to 45°C – conditions can support Legionella growth.
- Above 50°C – bacterial survival becomes increasingly limited as temperature rises.
- 60°C and above – Legionella does not survive under normal conditions.
For this reason, temperature control remains one of the traditional and most widely used methods of controlling Legionella within domestic hot and cold water systems.
❄️ What Temperature Does Legionella Grow At?
Legionella bacteria can multiply when water temperatures are between approximately:
20°C and 45°C
This temperature range is particularly significant when other favourable conditions are also present, such as:
- Stagnant or slow-moving water
- Biofilm
- Scale
- Sediment
- Corrosion products
- Poor water turnover
- Dead legs or redundant pipework
Keeping water temperatures outside this range helps reduce the opportunity for Legionella bacteria to multiply.
📏 UK Legionella Temperature Guidelines
HSE guidance provides clear temperature benchmarks for conventional hot and cold water systems.
Hot water storage
Hot water should generally be stored at:
60°C or above
Where calorifiers or hot water storage vessels are used, maintaining the correct storage temperature helps control Legionella within the system.
Hot water distribution
Hot water should reach:
At least 50°C within one minute at outlets
For healthcare premises, HSE guidance specifies a higher distribution temperature of:
55°C within one minute
Where thermostatic mixing valves (TMVs) are installed, temperatures should normally be assessed on the hot water supply feeding the TMV rather than relying solely on the mixed outlet temperature.
Cold water
Cold water should be maintained, where possible, at:
Below 20°C
Cold water temperatures above 20°C may indicate heat gain, insufficient turnover or another issue requiring investigation.
⚠️ Why Is Temperature Control Important?
Water temperature is one of the key factors influencing whether Legionella can multiply within a building’s water system.
Common temperature-related issues identified during Legionella risk assessments include:
- Hot water failing to reach 50°C within one minute
- Calorifiers operating below the required storage temperature
- Poor hot water circulation
- Excessively low hot water return temperatures
- Cold water exceeding 20°C
- Hot and cold pipework installed too closely together
- Inadequate pipe insulation
- Little-used outlets allowing water to stagnate
- Oversized cold water storage tanks
- Redundant pipework and dead legs
Temperature problems should therefore be investigated rather than simply recorded.
🔧 How to Maintain Suitable Water Temperatures
Effective Legionella temperature control usually requires a combination of monitoring, maintenance and good system design.
Typical measures include:
- Monitoring hot and cold water temperatures
- Maintaining hot water storage temperatures
- Checking hot water flow and return temperatures
- Monitoring sentinel outlets
- Checking representative outlets on a rotational basis
- Insulating hot and cold water pipework
- Preventing heat transfer between services
- Removing redundant pipework and dead legs
- Maintaining good circulation
- Ensuring adequate water turnover
- Flushing infrequently used outlets
- Maintaining calorifiers, storage tanks and associated equipment
Temperature monitoring results should be recorded as part of the site’s Legionella control programme.
🏢 Where Is Temperature Control Particularly Important?
Temperature control should be considered wherever a water system could create a foreseeable risk of exposure to Legionella.
This can include:
- Hotels
- Hospitals
- Healthcare facilities
- Care homes
- Residential buildings
- Offices
- Schools and universities
- Leisure centres
- Sports facilities
- Industrial premises
- Large commercial buildings
Particular attention should be given to buildings containing extensive water distribution systems, stored water, recirculating hot water systems or outlets that are used infrequently.
🚿 What About Thermostatic Mixing Valves?
Maintaining sufficiently high hot water temperatures must also be balanced against the risk of scalding.
Thermostatic mixing valves are often installed at outlets used by vulnerable people to reduce the temperature of the water delivered to the user.
However, fitting a TMV does not remove the need to maintain appropriate temperatures within the hot water distribution system.
The hot water supplying the TMV should still achieve the required Legionella control temperature.
📋 UK Legal Responsibilities for Legionella Control
Employers, landlords and others responsible for premises may have duties to assess and control the risk of exposure to Legionella.
Relevant UK legislation and guidance includes:
- Health and Safety at Work etc. Act 1974
- Control of Substances Hazardous to Health Regulations 2002 (COSHH)
- HSE Approved Code of Practice L8 – Legionnaires’ disease: The control of legionella bacteria in water systems
- HSG274 Part 2 – The control of legionella bacteria in hot and cold water systems
The duty holder should ensure that the risks associated with the water system are assessed and that appropriate control measures are implemented where required.
Temperature control is one method of achieving this but should form part of a wider water hygiene management programme.
✅ Key Legionella Temperatures at a Glance
| Temperature | Significance |
|---|---|
| Below 20°C | Legionella can survive but generally does not multiply |
| 20–45°C | Temperature range favourable for Legionella growth |
| 50°C | Normal minimum hot water outlet temperature within one minute |
| 55°C | Normal minimum hot water outlet temperature for healthcare premises |
| 60°C | Normal minimum hot water storage temperature |
These figures should always be considered alongside the design, operation and risk profile of the individual water system.
Final Thoughts
There is more to Legionella control than simply reaching one particular temperature.
The objective is to operate the water system in a way that limits conditions in which Legionella can multiply.
For conventional temperature-controlled systems, this generally means:
Keeping cold water below 20°C, storing hot water at at least 60°C and ensuring hot water reaches at least 50°C at outlets within one minute.
Regular monitoring, good water turnover, appropriate system design and effective maintenance are all essential parts of an effective Legionella control programme.
Need Help Managing Legionella Risk?
Source Water Compliance provides Legionella risk assessments, water hygiene consultancy and compliance support for organisations throughout the UK.
Whether you require a new Legionella risk assessment, a review of an existing water management programme or assistance investigating temperature failures, our experienced assessors can help you understand your water systems and identify appropriate control measures.
Contact Source Water Compliance today to discuss your Legionella compliance requirements.
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