CONTROL OF
LEGIONELLA BACTERIA
IN HOT AND COLD WATER SERVICES
The Health and Safety At Work Etc Act 1974
Control of Substances Hazardous to Health Regulations 2002
(as amended) (COSHH)
There are a variety of systems that supply hot and/or cold water services which, in the
past, have been associated with outbreaks of Legionnaires’ disease. These include not
only cooling towers but anything creating fine mists (aerosols) of water droplets such as
showers, spa baths, ornamental fountains and irrigation systems to name but a few.
Through maintenance and care of such systems, the growth of Legionella bacteria (the
causative organism of Legionnaires’ disease) can be effectively controlled.
WATER SYSTEMS
As the owner/operator of the business you are required to either take personal
responsibility or nominate in writing a responsible person with regard to the management
of any water system that could support Legionella bacteria. Such a person must be
competent i.e. have sufficient knowledge, training and experience of hot and cold water
systems and the Legionella hazard. You will also need to identify a deputy to cover in the
responsible person’s absence. In order to assist the responsible person or deputy the
services of an outside contractor (eg a water management company) may be obtained to
help maintain their duties under COSHH.
Risk Assessment
You must assess the risks to staff, service users and other persons likely to come into
contact with Legionella bacteria from your water systems. Particular attention must be
paid to the following points:

locations at which Legionella bacteria are likely to be present (eg water tanks,
pipework, shower heads);

the identification of all potential conditions which could result in its growth (eg
redundant pipework creating “dead legs”, water being held at a temperature of
between 20-45ºC, the presence of sludge/slime or other contaminants which may
be used as nutrients by the bacteria);

any means of creating breathable water droplets (aerosols) must be identified –
(eg shower heads, spa bath jets, spray from hosepipes etc);

circumstances where people may be exposed to such aerosols must be identified;

persons at particular risk (eg persons with weakened immune systems such as
the elderly).
Your risk assessment may well reveal a foreseeable risk of exposure to Legionella
bacteria. In this case, you must then produce a written control system for controlling the
risk of exposure.
2
Walsall MBC – Environmental Health
Written Control System
This must consist of the following:

an up-to-date schematic plan of the water systems within the premises;

instructions on the operation of each system. This should cover normal operating
procedures as well as action to be taken following plant breakdown or when a
shut down occurs for maintenance;

details of precautions to be taken to control Legionella bacteria and other
microbiological diseases.
Legionella bacteria thrive at temperatures between 20ºC and 45ºC.
They are
killed/controlled at higher temperatures and this is normally the method of control within
water systems.
Monitoring of Temperature Control Regime for Hot and Cold Water Services
Precautions should include the following:
Cold Water Tanks

supply cold water at 20ºC or below;

insulate the tank if there is the potential for it to warm up to over 20ºC;

keep a tight fitting lid on the tank to avoid contamination;

drain and inspect the tank annually;

ensure it is kept clean and free of scale/sediment;

the tank must not be oversized, causing water stagnation. Therefore, the tank’s
capacity must be sufficient for a 24-hour period only.
Calorifier (Hot Water Tank)

drain the tank annually to ensure sludge from the bottom of the tank is removed ;

set the temperature to operate to at least 60ºC;

ensure it is kept clean and free of scale/sediment;

most calorifier’s will experience varying zones of water temperature
(stratification), although the output temperature can be in excess of 60ºC. To
prevent this variation a shunt (stratification) pump should be fitted to the tank,
which will circulate the water inside. The pump should be operated for 1 hour per
day –usually by a timer – at the period of lowest consumption.
Pipework



where possible, minimise the lengths from boiler/cold water tank to
tap point;
keep hose pipes as short as possible. Ensure they are disconnected
and emptied of water when not in use.
the system must not have any dead legs. These are ‘dead ends’
within the pipework where water is not circulated, allowing water
3
Walsall MBC – Environmental Health
stagnation. A dead leg can be any length of pipe, anything twice the pipe
diameter or longer;

ensure irregularly used outlets are flushed weekly;

ensure hot water is distributed through pipework at a minimum of 50ºC. The hot
water should reach at least 50ºC within one minute when running the tap
otherwise a re-circulating pump may be required. This pump keeps the hot water
in the system circulating, to maintain a constant temperature. At tap points where
there is a foreseeable risk of scalding, thermostatic mixer valves (TMVs), which
fail to safe must be fitted. These ensure that although water is distributed to the
mixer valve at 50ºC or above, thereafter it is delivered at a maximum of 43ºC.
Where these are required, the TMV must be fitted to each individual service and
as close to the outlet point as possible. However, where vulnerable persons are
not expected to use the tap a mixer tap should be provided instead.
Further Important Controls

a sufficient de-scaling, cleaning and disinfection regime must be set out and
implemented.

shower heads, and taps and hosepipes should be thoroughly flushed through
weekly.

check the incoming mains cold water temperature on a six monthly basis
(preferably in summer and winter); the water temperature should not exceed
20○C.

check the water temperature at sentinel taps (furthest and nearest to the hot
water boiler system) on a monthly basis. Cold water should be below 20○C after
running for 2 minutes. Hot water should be at least 50○C within 1 minute. Water
supplies up to TMV points (where fitted) should also comply with this. The
temperature of hot water as it leaves and returns to the calorifier should be
measured. Outgoing water must reach at least 60○C and the returning
temperature (where appropriate) must reach at least 50○C.
ADVICE ITEMS
You are strongly advised to engage the services of a Water Treatment company to
conduct microbiological testing for the presence of Legionella bacteria.
Further advice can be obtained from the Health and Safety Executive’s Approved Code of
Practice and Guidance entitled “Legionnaires’ Disease, the Control of Legionella Bacteria
in Water Systems”, ISBN 07176 17726. This publication is available from HSE Books
directly by telephone, 01787 881 165 or via their website www.hsebooks.co.uk.
For spa pools and baths it is recommended that you refer to the Health Protection Agency
(HPA) guidance document entitled “Management of Spa Pools – Controlling the Risk of
Infection” ISBN 0 901144 80 0. You can obtain this publication from the HPA website at
www.hpa.org.uk.
4
Walsall MBC – Environmental Health