Legionnaires' Disease: The Control of Legionella Bacteria in Water Systems

1. Introduction

Legionaires’ Disease or Legionellosis is the term used for infections caused by Legionella pneumophila and other related bacteria. Legionella bacteria are only dangerous in respirable form and generally only to susceptible individuals where inhalation of the bacteria in aerosols or water droplets (typically <5mm) may cause severe pneumonia and, in extreme cases, death.

Legionella bacteria are widespread and found naturally in many aquatic environments, where they feed on algae and organic matter in sludge, sediment and silt. They tolerate a range of temperatures, although below 20°C and above 50°C they are dormant and above 60°C they will not survive.

When Legionella  bacteria enter man-made water systems they may proliferate under favourable conditions. If water droplets are then created and dispersed into the atmosphere then people in the vicinity may be at risk of inhaling the bacteria. To eliminate or reduce the risk, control measures must be in place to prevent the proliferation of the organism in water systems, and to minimise the generation of water droplets and aerosols.

2. Approved Code of Practice

A revised version of the Approved Code of Practice (ACoP) and Guidance, ‘Legionaires Disease: the Control of Legionella Bacteria in Water Systems’ (ISBN 0-7176-1772-6, commonly referred to as ‘L8’) was published in 2001. Compliance with L8 ensures compliance with duties under the Health and Safety at Work Act 1974, and the Control of Substances Hazardous to Health Regulations (COSHH) 2002.

L8 applies to:

  • Hot and cold water systems
  • Plant or systems containing water likely to exceed 20°C, which may release aerosols during routine operation or maintenance
  • Cooling towers
  • Evaporative condensers

This Policy Statement updates the previous policy, S8/01, and sets out the arrangements for controlling Legionella in the University’s water systems, plant and specialist equipment, in accordance with the revised ACoP L8.

3. Duty holders and responsibilities

(a)  Domestic hot and cold water systems

The control and management of Legionella in hot and cold water systems is a corporate responsibility and the role of Statutory Duty Holder rests with the University Estates Services. L8 allows the Duty Holder to obtain assistance from a competent contractor, and the University has engaged a specialist water treatment contractor.

(b)  Specialist departmental systems or equipment

Where departments possess and operate specialist water systems or equipment, which are independent of the domestic water supply (hence not an Estates Services responsibility) and which present a potential Legionella exposure risk, then the department must take on the responsibilities of the Duty Holder, summarised in section 4(a) below, and suitable arrangements must be in place to manage the risks.

Specialist advice is available and departments who require assistance in fulfilling their duties should contact the University Safety Office or Estates Services.

4. Control of Legionella

(a)  The broad requirements of L8 for controlling Legionella bacteria in water systems are:

(i)  appointment of a responsible person (in a managerial rather than technical grade)

(ii)  formal Legionella risk assessment with suitable and sufficient documentation of findings, including schematics detailing the water system

(iii)  ongoing review and reassessment of Legionella exposure risk

(iv)  development of a risk minimisation programme, a prioritised action plan and a mechanism for escalating remedial work where risk assessment and monitoring data indicate a risk

(v)  implementation and management of the programme

(vi)  development of formal procedures for inspection, maintenance and disinfection of water systems

(vii)  training of staff

(viii)  maintenance of suitable records.

(b)  The Estates Services is responsible for ensuring that risk assessments are carried out in systems under their control. Assessments should be reviewed at least biennially and when they may no longer be valid, for example when changes are made to the use of the building in which the water system is installed.

(c)  The Estates Services is responsible for the maintenance, monitoring, treatment, cleaning and disinfection of hot and cold water systems according to the guidance set out in L8 and the risk assessment for each system should detail these arrangements.

(d)  Where risk assessment identifies a significant risk, the Estates Services will arrange for the system to be disinfected immediately, either thermally or by chemical means. The system will then be monitored to ensure the efficacy of the treatment regime. If necessary, the regime will be modified until the risk of exposure to Legionella is reduced to acceptable limits.

5. Hot and cold water services

(a)  Water service systems must comply with the Water Supply (Water Fittings) Regulations 1999, and any subsequent amendments. Estates Services will ensure that only competent contractors are engaged for maintenance, repair, or replacement programmes and that only approved materials are used.

(b)  Estate Services will ensure that cold water storage is minimised, and this normally should be no greater than one working day’s average water consumption. Water use in buildings should be recorded annually. Estates Services will ensure that suitable measures are in place to protect cold water storage tanks and prevent excessive temperature increases in the cold water supply.

(c)  Storage calorifiers and recirculating hot water systems must store hot water at a minimum temperature of 60°C and deliver hot water of at least 50°C to the outlet. Estates Services is responsible for monitoring the temperature of these outlets in accordance with the regime set out in Table 1.

Consideration of the Legionella risks associated with calorifiers and central hot water systems must be taken into account during any hot water replacement programme. Wherever practicable, hot water storage vessels should be replaced with plate heat exchange systems or direct gas fired hot water heaters.

(d)  Where thermostatic mixing valves (TMVs) are installed these should be sited as close as possible to the point of use. As a general rule TMVs should not serve multiple outlets, but where this is absolutely necessary Estates Services will ensure that the pipework is kept as short as possible.


(i)  Point of use electric water heaters (POUWH) should be used in new and refurbishment projects wherever practicable. Estates Services is responsible for monitoring and adjusting the temperature of the outlets to ensure this is above 50°C (see Table 1). Departmental users must not tamper with these settings since any adjustment below 50°C may encourage the growth of Legionella bacteria. However any concerns regarding the temperature of the water may be referred to Estates Services for investigation and adjustment if necessary.

(ii)  The responsibility for maintenance and repair of all POUWHs lies with departments. Where faults are identified during routine monitoring these will be notified to the department, in writing, by Estates Services. Failure to undertake the appropriate repairs within a reasonable time (1 month) will result in the relevant heater being disconnected. Reconnection may only take place when the requisite repairs have been undertaken.

(f)  Domestic hot and cold water outlets, especially domestic showers, must be used regularly or at least on a weekly basis to prevent potential stagnation of the water supply. Building and facilities managers must identify to Estates Services any outlets that are used either intermittently (e.g. term time only or other seasonal use) or which are under-used. The Legionella risk assessment will be reviewed by Estates Services to determine whether a formal flushing regime is required or whether the outlet should be removed. Departmental managers must also apprise Estates Services of any significant change of use within their department that may adversely impact on the Legionella control programme.

(g)  Isolated outlets which, as a result of refurbishment, later demonstrate insufficient throughput and / or which test positive for Legionella bacteria on a recurrent basis should be removed.

6. Emergency showerheads

(a)  Laboratory drench showers

(i)  Drench showers are no longer specified for new buildings, unless activities present a significant risk of contamination to personnel. In this case activities should be carefully reviewed to eliminate, reduce or control the potential exposure to harmful agents by other means, in accordance with the eight principles of good practice set out under COSHH (see also UPS S6/14, Appendix 2). If drench showers are still identified as a requirement then the Safety Office should be consulted.

(ii)  Where drench showers are already installed the Estate Services is responsible for ensuring they are flushed through every six months and purged to drain using a method that does not create an aerosol. Detailed records must be kept and be available for inspection. If existing drench showers are no longer required they should be removed and the system capped off to the nearest junction to avoid dead legs. Estate Services will undertake the work and be responsible for updating the records.

(b)  Emergency eye wash stations

The Estate Services is responsible for ensuring that these are flushed and purged to drain on a six monthly basis, without creating an aerosol. Departments may wish, for reasons of hygiene and as an ongoing check of operation, to flush eye wash stations more frequently. However this may introduce an additional risk of exposure to Legionella bacteria. Weekly flushing is considered to represent no additional risk, whilst longer intervals between flushes may increase the risk. Therefore departments who elect to flush and purge emergency eye wash showers more frequently than the Estate Services programme, should do so on a weekly basis. They must ensure that their procedure does not create aerosols and that personnel undertaking the task are trained to do so. Appropriate records must be maintained.

7. Humidifiers and spray type air washers

(a)  The University’s policy has been to replace spray humidifiers and spray air washers with steam humidifiers. Departments who continue to operate such equipment should notify the Safety Office with comprehensive details of equipment still in use.

(b)  Existing spray humidifiers and spray air washers must be regularly inspected, cleaned, disinfected and maintained by the department - see Appendix 1.

(c)  There are currently no ultrasonic humidifiers under the control of Estates Services. Future installation of such equipment should be discouraged since it introduces a potential risk of Legionella exposure, demanding rigorous inspection and maintenance as described in Appendix 1.

(d)  Where departments continue to use ultrasonic humidifiers as part of their experimental equipment, then it is their responsibility to arrange for inspection and maintenance in accordance with Appendix 1, to clean and disinfect all wetted parts six monthly, with sampling of the ultrasonic mist for the total viable count (TVC) at three monthly intervals.

8. Other equipment which creates risk

(a)  Equipment such as water softeners, sprinkler and hose reel systems, lathe or machine tool coolant systems, horticultural misting equipment and indoor fountains and water features can also create risk.

(b)  Departments with any of the equipment described in Appendix 1 should maintain and clean it in accordance with the recommendations therein.

9. Other activities which create risk

(a)  Where departments design, manufacture, import or supply water systems that may create risk of exposure to Legionella bacteria (see Appendix 1 for examples) they must possess a copy of L8 and amongst other things ensure that the water system is so designed and constructed that it will be safe and without risks to health when used at work.

Further advice may be sought, via the University Safety Office, if there is doubt regarding the Legionella exposure risk of specialist equipment.

(b)  The department should provide adequate written information to users to enable safe use of the water system(s).

10. Cooling towers and evaporative condensers (including adiabatic systems)

(a)  There are no evaporative condensers in the University and none may be newly installed.


(i)  There is currently one cooling tower, located in the Clarendon Laboratory, which is notified to the Local Authority and the University Safety Office, but which has been decommissioned. This tower may not be reinstated and no new cooling towers may be installed.

(ii)  There is a miniature departmental cooling tower, located in the Thom Building, which is used for experimental purposes. This tower (and associated systems) must be inspected and maintained in accordance with the Approved Code of Practice and Guidance, L8.

In the case of this equipment, the responsible person must ensure that:

  • a detailed risk assessment is drawn up by a technically competent person (this may be the specialist contractor and department jointly)
  • assessments are updated annually or when no longer valid, e.g. when:
  • changes are made to the water system or its use
  • new information emerges about risks or control measures
  • monitoring indicates that control measures are no longer effective
  • a case of Legionnaires' Disease / Legionellosis is associated with the system
  • detailed records are kept of precautions taken, and these are available for inspection
  • all personnel who inspect, maintain and clean the system / equipment are trained and training records maintained
  • the Safety Office is contacted, immediately, with details of any suspected case of Legionnaires’ Disease / Legionellosis
  • notification has been made to the Local Authority, if necessary, in accordance with the Notification of Cooling Towers and Evaporative Condensers Regulations, 1992.

(c)  Adiabatic cooling systems are sometimes used as an alternative means of cooling / air conditioning. Although they are relatively simple and economically attractive in comparison to normal air conditioning (AC) systems, adiabatic systems introduce a potential risk of exposure to Legionella if used intermittently or not maintained properly. For example, the extreme hardness of the local water supply may result in excessive scaling and contamination, which may encourage the growth of Legionella. This may then necessitate a more costly, labour intensive Legionella management regime, offsetting any installation and operational savings. Therefore designers must carefully consider the local conditions and any implications for Legionella control during future operation and maintenance before specifying these systems in new building projects. The Safety Office should be consulted about any proposals to install adiabatic cooling systems in new buildings.

11. Training

Estates Services arranges training sessions and seminars, on an approximately quarterly basis, in conjunction with the University’s specialist contractor. Building and facilities managers should attend, as well as those individuals who are managerially responsible for specialist departmental equipment. Further information relating to the training programme may be obtained from Estates Services or the Safety Office.

12. Summary of departmental action

Departments must ensure that:

(a)  All specialised water systems / equipment are assessed for Legionella exposure risk.

(b)  Suitable regimes are in place for maintenance, disinfection, cleaning and monitoring of specialised water systems / equipment, and that records are kept.

(c)  Personnel who operate and maintain specialised water systems / equipment are suitably trained.

(d)  Point of use water heaters (POUWH) are maintained and repairs undertaken promptly when faults are reported by the Estates Services.

(e)  The Estates Services is notified of any intended, or actual, alteration to the domestic water system so that the system may be reassessed for risk and any changes recorded.

(f)  The Estates Services is notified of any hot or cold water outlet which is under-used or used intermittently, so that an appropriate management plan can be implemented.

(g)  The Safety Office is notified, upon receipt of this Policy Statement, with details of air spray washers or spray humidifiers still in operation.


March 2007