Health & Safety Guidance Notes: Control of Legionella Bacteria 

This note is not exhaustive in providing advice on the control of legionella bacteria in water systems.  It is strongly recommended that reference be made to The Health and Safety Executive's Approved Code of Practice & guidance document -Legionnaires' disease - The Control of legionella bacteria in water systems (L8). (HSE Books PO Box 1999, Sudbury, Suffolk  CO10 2WA. Tel. No. 01787 881165).  The HSE publication gives practical advice on how to comply with the law.

1. Introduction:  Legionnaires Disease is a potentially fatal form of pneumonia which can affect anybody, but which principally affects those who are susceptible because of age, illness, immunosuppression, smoking etc.  It is caused by the bacterium Legionella pneumophila and related bacteria that can be found naturally in environmental water sources such as rivers, lakes and reservoirs, usually in low numbers.  As they are commonly found in environmental sources they may also be found in purpose built water systems such as cooling towers, evaporative condensers and whirlpool spas and hot and cold water systems.  If conditions are favourable the bacterium may grow creating conditions in which the risk from legionnaires' disease is increased. 
2. Duties under the law:
   • Identify and assess the sources of risk
   • Prepare a scheme (course of action) how you intend to control the risk from legionella by:
   • Providing an up-to-date plan or schematic diagram of your system including associated pipe work, valves and pumps etc.
   • Appointing a person to be managerially responsible (responsible person) for the prevention and control of risks from legionella
   • Describing the safe and correct operation of the system
   • Describing what control measures and other precautions will be used and;
   • Detailing what checks will be carried out on the control scheme and how often these checks will be carried out.
3. Legionella Control - Hot & Cold Water Systems:
   • Control Measures:
     • One way to minimise the growth of legionella is to store hot water above 60C and distribute it at above 50C.  However, care is needed where water runs hot. The risks of scalding should be assessed and appropriate measures taken to prevent burns, e.g. warning notices and/or thermostatic mixing valves (TMVs) on taps.
     • Where TMVs are fitted these need to be placed as close to the point of use as possible.  Ideally a single TMV should not serve multiple tap outlets but, if they are used, the mixer water pipe work should be kept as short as possible.
     • Water systems should be designed to avoid conditions that favour the growth of legionella by ensuring adequate insulation of storage tanks and pipes, using materials that do not encourage growth of legionella and protecting against contamination by fitting storage tanks with lids.
     • Water systems need to be routinely checked and inspected by a competent person.  E.g. an annual visual inspection of the cold-water storage tank should check that the tank/lid is in good condition, that there is good thermal insulation to protect it from extremes of temperature and that the insect screen is intact on the water overflow pipe.  The water should not contain any debris or contamination and if considered necessary then the tank should be cleaned and disinfected and any faults rectified.  If any debris or vermin is found then inspection will need to be more frequent.  Also the calorifiers should be drained and checked for debris in the base.
     • Risk assessments should be reviewed regularly.
     • Water stagnation can encourage conditions that favour growth of legionella. It is therefore advisable to remove dead runs in pipe work from the system, flush out seldom used shower heads, taps and remaining dead legs periodically (weekly), and to remove any dirt or limescale.  Showerheads should be dismantled, cleaned and descaled at least quarterly.
     • Water temperatures in the sentinel taps (not taps controlled by TMVs) should be checked monthly to see if: hot water has reached 50C after one minute and the cold water is below 20C after two minutes.
     • Routine microbiological monitoring of H&C water systems is usually not necessary however taste, odour and clarity of water might identify that a problem exists and then the system should be fully investigated including microbiological sampling.
     • Other water treatment methods include copper/silver ionisation and chlorine dioxide.
4. Legionella Control - Cooling Towers & Evaporative Condensers:
   • Notification:
     • There is a requirement to notify individual cooling towers/evaporative condensers to the relevant local authority.  (Environmental Health, North Shropshire District Council, Edinburgh House, New Street, Wem SY4 5DB) and also advise when and if such devices are no longer in use.
5. Duties under the Law: As described in part 2 above.
6. Monitoring and inspection activities should include (not exhaustive):
   • Daily checks to ensure that the biocide dispensing equipment is operational
   • Weekly Monitoring  of microbiological activity (aerobic bacteria) by use of dip slides - "7" below for action levels.
   • Identifying changes in water chemistry by checking suspended solids and pH etc. weekly.
   • The inspection of the condition of sprays/troughs, eliminators, pack, pond, immersion heater, fans and sound attenuators at least on a monthly to three monthly basis, according to risk.
   • Periodic sampling in addition to routine sampling of aerobic bacteria, for the presence of legionella by UKAS accredited laboratories. (at least quarterly) - "7" below for action levels.
   • Disinfecting, cleaning and desludging of cooling towers, which should be undertaken at least twice a year or more frequently dependent upon operating conditions or risk assessment conclusions.
7. Action levels following microbial monitoring for cooling towers:

   8.    Water Treatment Contracts:

• NB It has also frequently been found that operators of water cooling towers/systems are unclear as to the precise terms of their contracts with their water treatment company.  Some water treatment companies only have a remit limited to provide biocidal treatment of the water, with no-one responsible for implementing the other equally important areas of control (such as the checking and cleaning of drift eliminators, the maintenance of tower condition etc.)

   9.    Additional information:

Controlling Legionella in Nursing and Residential Homes

Essential information for providers of residential accommodation

A guide for employers

   10.   Main legislative requirements:

• The Control of Substances Hazardous to Health Regulations 2002 (COSHH)  
• The Notification of Cooling Towers and Evaporative Condensers Regulations 1992

Guidance Notes - Printable version