Site Policy & Management · Mandatory · Construction

Legionella / Water Hygiene Monitoring Log

A monitoring log for legionella controls in construction site water systems including welfare facility showers and hot water storage. Records weekly temperature checks (cold water below 20 degrees C, hot water above 50 degrees C at draw-off, stored hot water above 60 degrees C), flushing of infrequently used outlets, and corrective actions. Monitoring records must be retained for 5 years under ACoP L8.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. L8 ACoP / COSHH 2002 / HSWA 1974 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

Legal basis	L8 Approved Code of Practice (ACoP) / COSHH Regulations 2002 / HSWA 1974
Temperature controls	Cold water <20°C, hot water >50°C at draw-off, stored hot water >60°C
Monitoring frequency	Weekly temperature checks at representative sentinel points
Record retention	5 years for monitoring records, 2 years for risk assessment (or until superseded)
Risk range	Legionella proliferates between 20°C and 45°C — the danger zone
Enforcing authority	Health and Safety Executive (HSE) / Local authority environmental health

1. Legionella on Construction Sites — The Welfare Facility Risk

Legionella bacteria thrive in warm, stagnant water systems — and construction site welfare facilities present exactly these conditions. Shower blocks that sit idle over weekends, warm water stored in tanks without adequate temperature control, and pipework with dead legs where water stagnates all create an environment where legionella can proliferate to dangerous levels. When contaminated water is aerosolised through a shower head or tap, workers inhale the bacteria, which can cause Legionnaires' disease — a severe and potentially fatal form of pneumonia.

The key risk factors for legionella growth on construction sites are: stagnation of water in systems that are not in regular use, water temperatures between 20°C and 45°C (the ideal growth range), accumulation of scale, sediment, and biofilm in tanks and pipework, spray generation from showers and taps, and low usage patterns — particularly over weekends, holidays, and during site shutdowns. The L8 Approved Code of Practice requires a risk assessment and, where a risk is identified, the implementation of a control scheme with regular monitoring.

2. Monitoring Log Content

The Legionella / Water Hygiene Monitoring Log must record the results of all temperature checks, flushing activities, and control measures. The following table sets out the information that should be captured in the log.

Field	Detail
Site reference	Project name, site address, and welfare facility location
System description	Description of the water system (e.g. welfare unit hot and cold supply, shower block, storage tank)
Risk assessment date	Date of the most recent legionella risk assessment for the site water systems
Responsible person	Named individual responsible for implementing the water hygiene control scheme on site
Date	Date of each monitoring check
Cold water temperature	Temperature recorded at cold water outlets — must be below 20°C
Hot water temperature at draw-off	Temperature recorded at hot water outlets within one minute of running — must be above 50°C
Stored hot water temperature	Temperature of water in storage vessels — must be above 60°C
Infrequently used outlets flushed	Confirmation that outlets not used for 7 or more days have been flushed for at least 2 minutes before use
Deviation noted	Record of any temperature readings outside the required parameters, with details of corrective action taken
Checked by	Name and signature of the person carrying out the monitoring check
Annual review	Confirmation that the risk assessment and control scheme have been reviewed within the past 12 months
Record retention	Monitoring records retained for 5 years, risk assessments retained for 2 years or until superseded

3. Common Mistakes

Not flushing infrequently used outlets

Outlets that have not been used for 7 or more days must be flushed for at least 2 minutes before use. This is a critical control measure that removes stagnant water from the system. On construction sites, welfare facilities are often unused over weekends, bank holidays, and during site shutdowns. Failing to flush before the facility is brought back into use allows legionella that has proliferated in stagnant, warm water to be aerosolised when workers first use the showers or taps.

Allowing hot water to be stored below 60 degrees Celsius

Hot water must be stored at 60°C or above to prevent legionella growth. Water storage tanks in welfare units must be checked regularly to ensure the thermostat is set correctly and the heating element is functioning. If stored water drops below 60°C, legionella can colonise the tank and seed the entire distribution system. Temperature checks of stored water should be part of the weekly monitoring routine.

4. Frequently Asked Questions

Does L8 apply to small construction site welfare facilities?▾

Yes — L8 applies to all work premises where there is a reasonably foreseeable risk of legionella exposure, and this includes construction site welfare facilities. The level of control required must be proportionate to the risk. Low-risk systems (e.g. a simple cold water supply with no storage) need only basic controls such as regular flushing and preventing stagnation. Higher-risk systems — such as a shower block with warm water storage — require active temperature monitoring, a written control scheme, and regular recorded checks.

What should I do if a temperature reading is outside the required range?▾

If cold water is above 20°C or hot water is below 50°C at draw-off, or stored water is below 60°C, the deviation must be recorded in the monitoring log and corrective action taken immediately. This may include adjusting thermostats, repairing or replacing heating elements, flushing the system, or investigating the cause of the deviation. If temperatures consistently fall outside the required range, the risk assessment should be reviewed and additional control measures considered, such as thermal disinfection or engineering modifications to the system.

Who is the responsible person for legionella control on a construction site?▾

The duty holder is the employer or self-employed person who has control of the premises — on a construction site, this is typically the principal contractor. The duty holder must appoint a named responsible person to implement the water hygiene control scheme on site. This person must be competent and have sufficient authority to ensure the control measures are implemented. On larger sites, this role may be delegated to the site manager or facilities coordinator, but the duty holder retains overall responsibility.

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