Most frequent questions and answers

Legionella is a pathogenic group of Gram-negative bacteria that is rod-shaped.

It is a natural inhabitant of water and can be detected in rivers, lakes, and streams.

Around 61 species of Legionella have been identified.

Legionella are classified into 70 serogroups.

Serogroup 1 is the dominant serogroup and accounts for approx. 84% of human infections worldwide and can also cause Legionnaires Disease.

L. pneumophilia is responsible for approximately 90% of Legionellosis cases.

When the bacteria enters water systems in the built environment, conditions can often favour and encourage significant growth and reproduction to levels which can cause bacterial pneumonia and be fatal to humans. As a result, Legionella is considered as a biological hazard and is listed under the COSHH Regulations. This defines the need for a suitable risk assessment to cover water systems in the work place.

Legionellosis is the name for a group of illnesses associated with Legionella bacteria. There are three main illnesses caused by the bacteria

  • Legionnaire’s disease
  • Pontiac Fever
  • Lochgoilhead Fever

All types of infection are caused by Legionella pneumophila, although Legionella micdadei is responsible for Lochgoilhead fever.

Legionnaires’ disease is a potentially fatal form of pneumonia caused by the Legionella bacteria. There are actually several pneumonia-like diseases caused by different types of Legionella bacteria, known as Legionellosis.

Legionnaires disease occurs as a result of infections caused by the Legionellaceae family of bacteria. It is a form of pneumonia which results in around 250 identified cases a year and can prove fatal, especially to the elderly or those prone to respiratory problems.

Legionella is ubiquitous and found in;

  • Lakes
  • Rivers
  • Soils
  • Man made systems
  • Engineered water services

However, the conditions are rarely right for people to catch the disease from these sources. Outbreaks of the illness occur from exposure to legionella growing in purpose-built systems where water is maintained at a temperature high enough to encourage growth, e.g. cooling towers, evaporative condensers, hot and cold water systems and spa pools used in all sorts of premises (work and domestic).

They also require a supply of nutrients to multiply, sources include algae, amoebae and other bacteria. The presence of sludge, sediment, scale and other material within the system, together with biofilms, are also thought to play an important role in harbouring and providing favourable conditions for Legionella bacteria to grow.

People contract Legionellosis by inhaling small droplets of water (aerosols), suspended in the air, containing the bacteria. Certain conditions increase the risk from legionella if:

  • the water temperature in all or some parts of the system may be between 20-45 °C, which is suitable for growth
  • it is possible for breathable water droplets to be created and dispersed e.g. aerosol created by a cooling tower, or water outlets
  • water is stored and/or re-circulated
  • there are deposits that can support bacterial growth providing a source of nutrients for the organism e.g. rust, sludge, scale, organic matter and biofilms

Legionellosis is a collective term for diseases caused by legionella bacteria including the most serious Legionnaires’ disease, as well as the similar but less serious conditions of Pontiac fever and Lochgoilhead fever. Legionnaires’ disease is a potentially fatal form of pneumonia and everyone is susceptible to infection. The risk increases with age but some people are at higher risk including:

  • people over 45 years of age
  • smokers and heavy drinkers
  • people suffering from chronic respiratory or kidney disease
  • diabetes, lung and heart disease
  • anyone with an impaired immune system

The bacterium Legionella pneumophila and related bacteria are common in natural water sources such as rivers, lakes and reservoirs, but usually in low numbers. They may also be found in purpose-built water systems such as cooling towers, evaporative condensers, hot and cold water systems and spa pools.

If conditions are favourable, the bacteria may grow increasing the risks of Legionnaires’ disease and it is therefore important to control the risks by introducing appropriate measures outlined in Legionnaires’ disease – The control of legionella bacteria in water systems – L8 (Fourth edition) for UK and Health Protection Surveillance Centre (HPSC) – National Guidelines for the Control of Legionellosis in Ireland 2009 for Ireland.

If you were to contract Legionnaires’ disease it would need to be treated with antibiotics. Without treatment it can be fatal. Many antibiotics are highly effective against Legionella bacteria. The two most potent classes of antibiotic are the macrolides and the quinolones. Other agents that have been shown to be effective include tetracycline, doxycycline, and minocycline.

Yes, there are over 61 different species of legionella bacteria. However, Legionella pneumophila is considered the most dangerous as it causes about 90% of the cases of infection. Around 16 different sub groups of legionella pneumophila have been reported as the cause of infection. However, Legionella Pneumophila Serogroup 1 is the most associated with Legionnaires’ disease in the UK.

It is impossible to tell who is most at risk just by looking at people, as many conditions that could increase the risk are not visible. Generally speaking though, everyone is susceptible; however, the risk increases with:

  • Suppressed immunity
  • Existing illness
  • Chronic respiratory disease
  • Chronic kidney disease
  • Lung & heart disease
  • Smokers
  • Age 45+


  • Cough
  • Shortness of breathe



  • Aches
  • Pains
  • Ataxia



  • Nausea
  • Diarrhoea
  • Vomiting


Fever Symptoms

  • Headache
  • Chills
  • Tiredness

Infection can be fatal in approximately 12% of reported cases. This rate can be higher in a more susceptible population.

The milder forms of the diseases known as Pontiac fever or Lochgoilhead fever are usually less severe, but people still have flu like symptoms.


Legionnaires’ disease is reportedly not contagious and cannot be passed from person to person. The disease is transmitted by inhaling the aerosol of an infected water supply, not usually by infected persons. Legionella is different from Coronavirus (e.g. Covid-19, SARS) & Swine Flu which are highly contagious.

However a case in Portugal has suggested that the infection may, in very rare cases be able to spread between individuals.

The case in question occurred on November 2014 when a maintenance worker contracted legionnaires disease following a large outbreak at a cooling tower complex in Vila Franca de Xira in western Portugal.

Having returned to a home he shared with his elderly mother in Porto, which was almost 190 miles from the site of the outbreak, he began to develop symptoms. Around two weeks after being transferred to hospital the man’s mother who had helped care for him also became ill. Sadly both the mother and the son succumbed to the illness and passed away.

Testing later confirmed that the mother’s illness was caused by the identical strain of legionella bacteria which her son had been infected with. Tests carried out on the home showed there was no signs of legionella within the water systems, this combined with the fact the mother had never visited the original site of the outbreak has led investigators to conclude that the mother most likely became infected through direct contact with her son.

Despite this case, experts still believe the chances of person-to-person transmission is highly unlikely and the main threat is still from contaminated water systems which should be properly maintained to help reduce the risks of legionella bacteria developing.

As a person who is responsible for water systems you have certain duties under Health and Safety law. The Health and Safety at Work Act 1974 (HSWA), Control of Substances Hazardous to Health Regulations 1999 (COSHH) and Management of Health and Safety at Work Regulations 1999 (MHSWR) all cite the HSE’s Approved Code of Practice L8 (Fourth edition) as the recommended guidelines for the management of risk of exposure to Legionella.

Under Health and Safety Law it is your duty to consider the risks from Legionella that could affect your employees and members of the public and take suitable precautions, which include;

  • Identify and assess the risk
  • Prepare and implement a course of action to prevent or control the risk
  • Appoint a person to be managerially responsible
  • Keep records and ensure effective control


The Health and Safety at Work etc Act 1974 places duties and responsibilities on employers and employees to ensure, so far as reasonably practicable, the health and safety at work of the employees and general public.

A suitable Legionella risk assessment is required to cover water systems in any commercial premise. This includes rented housing stock particularly where communal services are present.

It’s a legal duty to carry out an assessment to identify & assess whether there is a risk posed by exposure to legionella or other waterborne bacteria from the water systems or any work associated with it.

As an employer, or a person in control of a premises, you’re responsible:

  • for health & safety and need to take the right precautions to reduce the risks of exposure to legionella or other waterborne bacteria
  • to make an assessment of the risks to other people not in their employment who may be affected by the work activity
  • to regularly review the risk assessment and make any necessary changes as a result of the review
  • to have access to competent help in applying the provisions of health and safety law as per The Management Regulations
  • to introduce a course of action (i.e. a written scheme), that will help you to manage the risk from legionella or other waterborne pathogens, such as Pseudomonas, by implementing effective control measures

Carrying out a risk assessment is your responsibility. You may be competent to carry out the assessment yourself but, if not, you should call on help and advice from either within your own organisation or from outside sources

In short – if you have water on site that people can be exposed to, you need to assess and manage the risk from Legionella bacteria.

Any undertaking involving a work activity and to premises controlled in connection with a trade, business or other undertaking where water is used or stored and where there is a means of creating and transmitting water droplets which may be inhaled, thereby causing a reasonably foreseeable risk of exposure to Legionella bacteria requires a Legionella Risk Assessment. 

The majority of sites/businesses will require a Risk Assessment to comply with the Approved Code of Practice for Legionella L8 (Fourth edition) & subsequent Guidance HSG274; however, Healthcare Premises should comply with Health Technical Memorandum (HTM 00, HTM 04-01, Parts A, B, C & D08). We would also recommend that the Risk Assessments carried out in Healthcare Premises are Water Hygiene Risk Assessments, that take into account all types of water quality risks, e.g. Other Waterborne Pathogens (Pseudomonas Aeruginosa, Cryptosporidium etc.), Backflow issues, Cross Contamination issues.

Risk assessment is an ongoing process which should be continually reviewed and updated as and when there are changes, such as;

  • changes to the water system or its use;
  • changes to the use of the building or part of the building in which the system is installed;
  • changes to the availability of information about risks or control measures;
  • indications that control measures are no longer effective;
  • new construction works or system modifications planned; or
  • changes to the key personnel, contractors and service providers


Examples: For simple assessments of inherently low risk water systems, the risk review could be performed by the competent person providing they have the appropriate level of competence to do so.

However, for complex water systems with inherently higher risks, such as cooling towers and for water systems in healthcare, or where additional expertise is required, it is helpful to have a periodic review process involving competent help, for example, regular formal review of the performance of the risk control measures with an appropriate specialist independent consultant or with a hospital Authorising Engineer being present at water safety group (WSG) meetings.

This would typically range from monthly to annually dependent upon the perceived risk. The output of this review process is a determination of the need for formal reassessment of the risk


Landlords who provide residential accommodation, as the person in control of the premises or responsible for the water systems in their premises, have a legal duty to ensure that the risk of exposure of tenants to legionella is properly assessed
and controlled. This duty extends to residents, guests, tenants and customers. They can carry out a risk assessment themselves if they are competent, or employ somebody who is.

Where a managing (or letting) agent is used, the management contract should clearly specify who has responsibility for maintenance and safety checks, including managing the risk from legionella. Where there is no contract or agreement in place or it does not specify who has responsibility, the duty is placed on whoever has control of the premises and the water system in it, and in most cases, this will be the landlord themselves.

By law, landlords must:

  • Ensure all tenants are protected from the risked posed by Legionella
  • Conduct a Legionella risk assessment
  • Introduce any necessary measures that reduce the risk posed by Legionella to your tenants


Landlords who prepare a “welcome pack” for tenants when they move in should include a request to flush out the water system, even if weekly flushes have been completed while the property has been vacant and once more prior to the tenant’s check-in.

Refer to: http://www.hse.gov.uk/legionnaires/legionella-landlords-responsibilities.htm

Depends on your Tenancy Agreement.

Typically the Landlord is responsible for carrying out a Risk Assessment. The Tenant should then be advised by the Landlord of their Responsibilities of maintaining the water systems as per the Risk Assessment.

Landlords who prepare a “welcome pack” for tenants when they move in should include a request to flush out the water system, even if weekly flushes have been completed while the property has been vacant and once more prior to the tenant’s check-in.

There are numerous measures that can be adopted to create water systems in the built environment that are hostile to the growth of Legionella. Most traditionally, temperature is used to control Legionella. Wherever possible, temperature should be the initial line of defence used to control Legionella growth in a system.

Carrying out a Risk Assessment will help you identify the risks and what should be implemented to help you eliminate or manage them. Findings from the risk assessment that can be used in producing a Scheme of Control / Written Scheme.

Cold Water – cold water is stored in tanks at temperatures close to the supply and ideally <20°C. The whole distribution system will ideally achieve <20°C within two minutes of turning on a tap.

Hot Water – hot water is stored & distributed ≥60°C from Calorifiers and ≥50°C throughout any circulating hot water system. Localised failure in circulation can increase risk and can often be identified by slow or delayed temperature increase when turning on a tap. Non-circulating systems are targeted to reach a minimum of 50 °C within one minute of turning on the hot water tap.

Chemical control: The use of chemicals can be used as the last line of defence, and we will always explore the fundamental measures for control and management before embarking upon or recommending any chemical treatment programme for domestic systems.

Stagnation: Stagnation can be prevented by introducing routine flushing programmes and reducing the volumes of stored water.

To reduce the possibility of increasing the risk of exposure to Legionella bacteria, controls should be introduced which do not allow proliferation of the organisms in the water system and reduce exposure to water droplets and aerosol.

HSG274 Part 2 gives guidance on developing programmes of regular routine checks to confirm that the above temperatures are being achieved. Records of these results will help assess any risk arising from inconsistency in control. In some cases, methods other than temperature, or in addition to temperature, are used, for example, biocides or other chemical or physical controls.

If you get a legionella positive result you should not panic! If Legionella is identified in your system there are many measures that you can take to eradicate it. Measures such as thermal disinfections, temperature management and chemical disinfections can be used to clean your system. You do not need to report a Legionella positive result to the Environmental Health or your Local Authority. If you obtain a Legionella positive result and need assistance or support contact us today.

A Cold Water Storage Tank (CWST) should only be cleaned & disinfected when required, such as:

  • build up of sediment deposits
  • slime accumulation on the internal walls and/or base
  • traces of debris or vermin
  • stagnation on stored water surface
  • CWST or associated system is substantially altered
  • when an outbreak has occurred or is suspected
  • Sampling indicates elevated bacteriological counts


All tanks should be inspected on an annual basis (in the Summer).

There is no legislation which defines that you must clean your cold water storage tanks on an annual basis.

The HSC Approved Code of Practice for Legionella L8 (Fourth edition) is only relevant in circumstances where the Health & Safety at Work etc Act 1974 applies, therefore most domestic property is exempt from regulation. The risk from domestic property is viewed to be very low at this time.

The cost of a risk assessment is entirely dependent on the amount of water services in use at the property. We offer a free consultancy meeting to assess your needs.

The two main pieces of legislation & regulation are the Health & Safety at Work Act (1974) and the Control of Substances Hazardous to Health Regulation (2001). Companies that fail to comply with government guidance may be prosecuted under either of these regulations.

These are supported by the Approved Code of Practice for Legionella L8 (Fourth edition) and HSG274.


Water Regulations

Most frequent questions and answers

The Water Supply (Water Fittings) Regulations and Water Supply (Water Fittings) (Scotland) Byelaws, play an important role in protecting public health, safeguarding water supplies and promoting the efficient use of water within customers’ premises across the UK.

They set legal requirements for the design, installation, operation and maintenance of plumbing systems, water fittings and water-using appliances. They have a specific purpose to prevent misuse, waste, undue consumption or erroneous measurement of water and, most importantly, to prevent contamination of drinking water.

These Regulations and Byelaws apply in all types of premises supplied, or to be supplied with water by a water company (the legal term for a water company is water undertaker – e.g. NI Water).

They apply from the point where water enters the property’s underground pipe (usually at the stop tap at the property boundary), to where the water is used in plumbing systems, water fittings and water-using appliances.

These regulations do not apply where a property uses a private water supply and does not have a supply of water from a water company. If a top up supply, from a water company, is in place full regulations/byelaws would apply (e.g. Fluid Category 5 backflow protection).

A legal duty is placed on all users, owners or occupiers and anyone who installs plumbing systems or water fittings and water-using appliances to ensure they are installed and used in accordance with these regulations and byelaws.

Advanced notice must be given of proposed installations in specific cases, so architects, building developers and plumbers have to follow these regulations and byelaws on behalf of future owners or occupiers.

Your plumbing systems, water fittings and water-using appliances must be installed, maintained and used to comply with the Water Fittings Regulations or Scottish Water Byelaws.

  • You must prevent contamination of drinking water.
  • You must use water efficiently.
  • You must give advanced notification of installation work, in specific circumstances.

Water Undertakers (the legal name for water suppliers) are duty bound to enforce the Water Fittings Regulations and Scottish Water Byelaws within their appointed water supply areas. e.g. NI Water in Northern Ireland.

They will undertake inspections of new and existing installations to check that the regulations and byelaws are being met.

Where contraventions of the Water Fittings Regulations and Scottish Water Byelaws are found, the water supplier will require them to be remedied as soon as practicable. Where breaches pose a risk to health or there is a significant waste of water, the water supply to the premises may be disconnected immediately to protect public health and prevent waste or damage to premises.

It is a criminal offence to contravene the regulations or byelaws and offenders may face prosecution. Those found guilty will have a criminal record, be fined and may have to pay costs.

The Water Supply (Water Fittings) Regulations and Scottish Water Byelaws only allow for an arbitrator to be involved in two specific circumstances.

  1. Where a water supplier has unreasonably withheld their consent in regards to an advanced notice of proposed installation work under Regulation or Byelaw 5.
  2. Where a water supplier has unreasonably refused to apply for a relaxation to the regulator.


However water suppliers normally have a policy to resolve disputes with customers. You should contact your water suppliers for details of their policy or procedure

Only the ‘person designated in writing by a water undertaker (the legal name for water suppliers)’ are authorised to enter premises. 

However this is only for very specific purposes and in relation to enforcing the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws, they are allowed as part of that work to carry out inspections, measurements or tests.

However if you do not allow them to enter they can seek a Magistrate’s Warrant from the courts which will allow them to enter.


Backflow & Cross Contamination

Most frequent questions and answers

Backflow is an unwanted flow of water in the reverse direction.

It can be a serious health risk for the contamination of potable water supplies with contaminated/foul water.

The undesirable reversal of flow of water or other substances usually occurs through a Cross Connection into the consumer’s potable water system.

Cross Connection means:

  • any actual or potential physical connection between a public water system or the consumer’s water system
  • any source of non-potable liquid, solid, or gas that could contaminate the potable water supply by backflow – e.g. a by-pass line, which have to be agreed with the local water supplier


Backflow may be due to either:

  1. Back siphonage; or,
  2. Backpressure


Back Siphonage means:

  • backflow due to a reduction in system pressure in the supplier’s distribution system and/or consumer’s water system


Backpressure means:

  • a pressure on the consumer’s side of the service connection that is greater than the pressure provided by the public water system and which may cause backflow. This could be caused by a pump, elevated tank or piping, boiler, or other means

For a drinking water (potable water) supply to become contaminated via backflow, two things need to happen simultaneously:

  1. A physical link (cross-connection). This may be provided by direct plumbing connection or submerged inlet
  2. A pressure differential. This may be caused by high pressure on the contaminated side (backpressure) or a negative pressure on the supply side (back siphonage)

Cross Contamination is the process by which bacteria or other microorganisms are unintentionally transferred from one substance or object to another, with harmful effect.

For drinking water supply to become contaminated via cross contamination, a substance or object containing bacteria or other microorganisms (e.g. drain, splashing of fluids) must be transferred onto a water supply outlet or fitting (e.g. tap, shower).

There are many scenarios where this can happen, such as:

  1. If a flexible hose shower is too long it can be placed below the spillover level of the shower tray or bath, or make contact with the base of the shower unit or drain, it is possible that bacteria, including antibiotic-resistant organisms, could seed the outlet
  2. During cleaning of basins and taps, there is a risk of contaminating tap outlets with microorganisms if the same cloth is used to clean the bowl of the basin or surrounding area before the tap.


This is why it is vital to have the appropriate backflow protection in place as it will minimise the risk of backflow and cross contamination of water systems.


Fluid Categories

Most frequent questions and answers

Means a category of fluid described in Schedule 1 of the Water Supply (Water Fittings) Regulations and/or Scottish Water Byelaws

There are 5 Fluid Categories that are detailed below. This states their determination and backflow protection required with examples given.

Determination: Wholesome water supplied by a water undertaker and complying with the requirements of regulations.

Example: Mains drinking water tap.

Backflow Prevention: No protection required, unless connected to an appliance or system as below.

Determination: Water in fluid category 1 whose aesthetic quality is impaired owing to:

  • A change in its temperature
  • The presence of substances or organisms causing a change in its taste, odour or appearance, including water in a hot water distribution system



  • Mixing of hot and cold water supplies
  • Domestic softening plant (common salt regeneration)
  • Drink vending machines in which no ingredients or carbon dioxide are injected into the supply or distributing inlet pipe
  • Fire sprinkler systems (without anti-freeze)
  • Water cooled air conditioning units (without additives)


Backflow Prevention: Single check valve required. If supplied by high pressure (e.g. mains, boosted cold) then fit a double check valve to minimise valve failure

Determination: Fluid which represents a slight health hazard because of the concentration of substances of low toxicity, including any fluid which contains:

  • Ethylene glycol, copper sulphate solution or similar chemical additives, or
  • Sodium hypochlorite (chloros and common disinfectants)



  • Water in primary circuits and heating systems in a house (<45kWh output)
  • Domestic clothes and dishwashing machines.
  • Ice-making machines
  • Drink vending machines in which ingredients or carbon dioxide are injected
  • Commercial softening plant (common salt regeneration only)
  • Non-pressurised steam oven


Backflow Prevention: Double check valve or AUK2 air gap required.

Determination: Fluid which represents a significant health hazard because of the concentration of toxic substances, including any fluid which contains:

  • Chemical, carcinogenic substances or pesticides
  • Environmental organisms of potential health significance



  • Commercial pressurised primary circuits & central heating systems in other than a house
  • Fire sprinkler systems using anti-freeze solutions
  • Commercial clothes washing and dishwashing machines
  • Hose union tap, self-closing trigger at swimming pools
  • Pressure washing systems for cleaning commercial hire plant
  • Steam Boilers


Backflow Prevention:

  • RPZ (Reduced Pressure Zone) valve for backpressure
  • Type DB pipe interrupter for back siphonage

Note: see “What is Backflow?” FAQ for difference between backpressure & back siphonage

Fluid Category 5

Determination: Fluid representing a serious health hazard because of the concentration of pathogenic organisms, radioactive or very toxic substances, including any fluid which contains:

  • Faecal material or other human waste
  • Butchery or other animal waste
  • Pathogens from any other source



  • Gravity fed Primary heating systems (e.g. header/F&E tank)
  • Non-domestic hose union taps (e.g. used for animal washing)
  • Grey / Rain water recycling systems
  • Bedpan washers
  • Commercial clothes washing plant and dishwashing machines in health care premises
  • Slaughterhouse equipment
  • Water storage for agricultural and firefighting purposes
  • Any medical or dental equipment with submerged inlets.
  • Hospital dialysing machines.
  • Vegetable washing.
  • Sinks, urinals, WC pans and bidets
  • Pressurised steam oven


Backflow Prevention: Type AA or AB break tank or AUK3 air gap.