Potable Water Maintenance Program – Legionella FAQs

Updated: January 8, 2025

Legionella
Legionella Exposure
Potable Water Maintenance Program
Testing for the Presence of Legionella
Building Maintenance

1. Legionella

1.1 What is Legionella?

Legionella is a waterborne pathogen causing Legionnaires’ disease. Legionnaires’ disease is an illness characterized by pneumonia, caused by infection with Legionella species such as Legionella pneumophila. Another name for Legionnaires’ disease is legionellosis. For more information, please see Public Works and Government Services Canada, MD 15161 – 2013, Control of Legionella in Mechanical Systems.

1.2 Where does Legionella appear?

Legionella bacteria are widespread within the natural water environment (rivers, lakes, ponds, and reservoirs) and can be found in soils and mud. It can also be found within biofilm growing inside a building’s plumbing and given a suitable condition, it can form biofilm from which the bacteria may be released from taps, showerheads, and other points of discharge. For more information, please see Public Health Ontario, Legionella: questions and answers, 2nd edition.

1.3 What conditions favour the growth of Legionella?

There are a number of important factors that provide an environment for Legionella to multiply: water temperature, the presence of biofilm, water stagnation and the type of plumbing material/components present. For more information, please see Public Health Ontario, Legionella: questions and answers, 2nd edition.

Water Temperature required for optimal Legionella growth is between 25°C and 45°C.

Biofilms are slimes that form on surfaces in contact with water, such as the inside walls of water pipes, air conditioners, cooling towers, whirlpools, showerheads, taps and humidifiers.

Water stagnation or low flow During period of water stagnation or low flow, hot water temperature decreases and cold water temperature increases. A decrease in residual disinfectant levels can also occur which are factors that are favourable to the development of biofilm and can produce an environment in which Legionella amplifies. Facilities that have undergone extensive renovations over time may have redundant pipework/dead legs in which water can stagnate. Infrequently used fixtures can also allow water to stagnate.

Other factors

Inadequate disinfection in the building’s water systems can lead to the proliferation of Legionella.
Certain plumbing materials can favour biofilm colonization in potable water systems.

The University’s Water Maintenance Program was developed to address these factors. Testing is guided by the Public works and Government Service Canada MD15161-2013 Control of Legionella in Mechanical systems and the

Ontario Agency for Health Protection and Promotion (Public Health Ontario) Legionella: Questions and Answers 2nd Edition Toronto ON; Queens Printer for Ontario: 2019. The Legionella action concentrations are also in line with the Canadian, American and international standards.

1.4 What type of plumbing materials and do I have that type in my building?

Research has shown plastic and rubber materials found in plumbing components, such as flexible hoses or thermostatic mixing valves, are susceptible to such colonization. For more information, please see Public Health Ontario, Legionella: questions and answers, 2nd edition.

2. Legionella Exposure

2.1 What factors must be in place to create a risk of someone developing Legionnaires’ disease?

Legionnaires’ disease is principally acquired by inhaling minute aerosolized droplets of contaminated water or aspiration of fluid from the mouth or stomach into the lungs. It is not considered to be transmitted from person to person or from ingestion unless aspiration occurs. The mere presence of Legionella bacteria in a building’s water system is not sufficient to cause Legionnaires’ disease. Certain factors that increase the risk of someone acquiring Legionnaires’ disease include:

Conditions suitable for growth of Legionella, such as water stagnation, suitable water temperature (25°C – 45°C) and deposits that are a source of nutrients for the bacteria.
A means of creating and spreading inhalable droplets, such as showers or spray heads on taps.
Exposure of vulnerable persons (e.g., elderly, dialysis patients, smokers, newborn infants, persons with underlying medical conditions, or persons taking medications that weaken the immune system) to colonized water that is inhaled or aspirated into the lungs.

For more information, please see Public Health Ontario, Legionella: questions and answers, 2nd edition.

2.2 What about exposure in cold water?

Legionella in cold water is not a material risk as Legionella favours warm water, but in temperatures of 25-45°C, it can multiply and pose a health risk if other concurrent conditions are also present (e.g., warm water with mist such as showers or spray heads on taps).

2.3 How does this affect general occupants?

The presence of Legionella in the water is not a material risk to general occupants unless it is aerosolized. Also, the individual generally needs to be a member of the susceptible population to acquire Legionellosis as noted in Public Works and Government Services Canada, Control of Legionella in Mechanical Systems, the Public Health Ontario, Legionella: questions and answers, 2nd edition, Legionellosis: Key Considerations for Case and Environmental Exposure Investigation, and Center for Disease Control, Legionella (Legionnaires’ Disease). As per CDC, most healthy people exposed to Legionella do not get sick. People at increased risk of getting sick are:

People 50 years or older
Current or former smokers
People with a chronic lung disease (like chronic obstructive pulmonary disease or emphysema)
People with weak immune systems or who take drugs that weaken the immune system (like after a transplant operation or chemotherapy)
People with cancer
People with underlying illnesses such as diabetes, kidney failure, or liver failure

2.4 Am I “susceptible” to Legionella?

The University follows applicable public health guidance. We appreciate that persons may have specific medical considerations. Whether a person is susceptible to Legionella depends on a number of personal factors, including any pre-existing medical conditions or underlying diseases, age, smoker/non-smoker status, medication, etc. As such, it is not possible to determine if an individual is susceptible to Legionella without a detailed health assessment conducted by a medical professional. If you have personal concerns or questions regarding Legionella, please contact our Occupational Health Nurse at ehs.occhealth@utoronto.ca.

Our procedures as per the Potable Water Maintenance Program adhere to and/or exceed the requirements of Ontario Public Health in terms of when testing needs to be performed (e.g., Ontario Public Health does not set a threshold for testing water systems after a certain length of a building being unused or having low occupancy, the University has developed and applied a threshold based on Public Works and Government Services Canada, MD 15161-2013, Control of Legionella in Mechanical Systems document in order to adopt a systematic approach to controlling Legionella on our campus).

If you would like more information on legionella, please refer to:

Public Works and Government Services Canada, MD 15161-2013, Control of Legionella in Mechanical Systems, Page 48, under “3. Inhalation”.
Public Health Ontario, Legionella: questions and answers, 2nd edition, Page 23, question 19.
Public Health Ontario, Legionellosis: Key Considerations for Case and Environmental Exposure Investigation, Slide 15.
Centers for Disease Control and Prevention, Causes, How it Spreads, and People at Increased Risk.

We also appreciate that individuals may also have specific questions regarding legionella and their particular medical condition, and they are welcome to contact our Occupational Health Nurse at ehs.occhealth@utoronto.ca.

3. Potable Water Maintenance Program

3.1 What is the purpose of the Maintenance Program?

The purpose of each of the maintenance procedures described in the University of Toronto Potable Water Maintenance Program is to confirm the system is functioning effectively and providing safe potable water to users.

3.2 What does the Water Maintenance Program include?

The Maintenance Protocol is specific to the University of Toronto potable hot and cold water only. The ongoing operational maintenance at the point of use such as drinking fountains and water refill stations is not included in the University of Toronto Potable Water Maintenance Program.

3.3 How is flushing done? Are all taps opened and flushed?

Generally, all taps are opened and flushed however, flushing for each building is dependent on the size of the building. For building specific information, please contact ehs.office@utoronto.ca.

3.4 Is there a standard operating procedure when it comes to flushing of the buildings?

Yes, there is a flushing procedure that applies when there is a low-flow or shutdown conditions for 4 weeks. Since the University has returned to normal operating procedures, the procedures have been archived in Appendix A of the Water Management Program. In the rare circumstance where the University does re-enter a low-flow or shutdown condition, the procedure will be reviewed and updated accordingly.

4. Testing for the Presence of Legionella

4.1 Did any building test positive for the presence of Legionella?

Yes, the Water Maintenance Program’s testing has found the presence of Legionella in some buildings. As soon as Legionella is detected in a building, remediation measures are immediately undertaken as detailed below. Remediation may include closing off areas as necessary and not reopening them until retesting indicates results are within acceptable levels (green). We remediate any instances of the presence of Legionella as soon as possible and retest to ensure our control measures are successful.

For more information on remedial actions, please review the University of Toronto’s Potable Water Maintenance Program.

4.2 Where can I find results for my building/area?

Results for buildings can be found on the EHS webpage, Water Maintenance Program and Testing for Presence of Legionella, which is updated once a week and a report sent to the JHSC. General occupants can receive notification of orange and red results by subscribing to F&S Service Alerts. To subscribe to F&S Service Alerts please click here.

4.3 Where do I find information on when my building is being tested?

A Water Testing Schedule has been created to keep occupants updated on when each building will be tested. We encourage occupants to check the schedule regularly for the most up-to-date information on testing in their building. Due to the duration and complexity of flushing a system and the required waiting time, there may be situations where re-testing is scheduled only a day or two in advance.

4.4 How are water sources selected to be tested?

Water sources in a building are selected for testing with a view to cover a range of both source types and floors. If Legionella is found during this initial screening, the scope of water sampling is expanded when retesting is conducted. It is not necessary to test every single shower, faucet and pipe but rather to focus on areas where there is an increased potential for Legionella to grow. Showers that are part of the distribution loop get tested for functionality once a year and are not tested for Legionella at this time. Also, Legionella is generally not tested in lab water supplies as these are typically separate from the drinking water supply to the rest of the building.

4.5 How come we did not test all areas?

It is not necessary to test every single shower, faucet and pipe but rather to focus on areas where there is an increased potential for Legionella to grow. We do test more locations on a follow-up visit as required. After the tested locations are all green, the predictive/preventive maintenance plan comes into effect.

4.6 What are the benchmarking categories?

There are three benchmarking categories based on the total concentration of Legionella pneumophila:

Green: <10 GU/mL or CFU/mL*
Orange: 10 to 100 GU/mL or CFU/mL
Red: >100 GU/mL or CFU/mL

*GU=Genomic Units from qPCR; CFU=Colony Forming Units from Cell Culture

4.7 What does the University do for a green result?

For buildings that test green, not detected, normal operations can continue and follow the predictive maintenance procedure of annual testing. In some cases, results in the green category have low levels of Legionella (<10 GU/mL or <10 CFU/mL). We continue to take precautions whenever we find a detectable amount of Legionella, for example, flushing and retesting until Legionella is no longer detected.

4.8 What does an orange result mean?

Orange results indicates that normal operations can continue, however, flushing of the system is needed along with re-testing. For clarity, in the orange category, occupants can continue using the facilities.

Results are communicated to the JHSC as well as posted on the EHS webpage on Water Maintenance Program and Testing for Legionella. General occupants can receive notification of orange and red results by subscribing to F&S Service Alerts. To subscribe to F&S Service Alerts please click here.

4.9 What does a red result mean?

Red results indicate flushing of the system along with shutdown of the affected areas and re-testing. Remediation may require additional maintenance (e.g., replacing mixing valve, temporary increasing water temperature above operating values, etc.). The affected area is closed off and made inaccessible to occupants. Occupants can continue to use other facilities within the building.

4.10 What does a positive qPCR test result mean?

The qPCR technology measures the amount of DNA specific to Legionella pneumophila in a water sample so a positive qPCR test result means Legionella pneumophila was detected at the water source. Results are reported as the total concentration of Legionella pneumophila expressed in genomic units per millilitre (GU/mL), a measure that is intended to be similar to the colony forming unit per millilitre (CFU/mL) results that culture testing provides. To minimize the presence of DNA from dead, non-viable Legionella pneumophila in a sample inflating the test result, the water sample is treated with an enzyme to degrade the DNA from dead, non-viable Legionella pneumophila as part of the measurement process. In some instances, the qPCR result may still be higher than what culture testing would obtain since the qPCR system measures the DNA from all living, viable Legionella pneumophila in a sample, both culturable and non-culturable. Water sources with positive qPCR results are monitored over time with follow up qPCR testing to determine if levels are climbing, descending, or remaining static and to inform the mitigation and remediation process. In certain circumstances, additional testing including culture testing will be considered on a case-by-case basis.

4.11 For buildings that are continuously testing orange/red, are there any considerations to conduct a culture test?

There are instances where qPCR may provide a higher result than culture testing due to the presence of live, but non-culturable Legionella. The focus is to eliminate all traces of Legionella in the system, regardless if it is considered culturable or not, as a positive result indicates the Legionella may regrow.

4.12 How are eyewash being tested?

Eyewashes are flushed weekly by the lab occupants.

Eyewashes use cold or tepid water. Tepid water is a mix of hot and cold water that is regulated by a mixing valve. Tepid eyewashes tend to be found in labs that have been renovated more recently. Cold water eyewashes tend to be found in older labs. Testing for Legionella primarily focuses on the hot water system in buildings as this is where Legionella thrives, so testing of eyewashes is focused on tepid systems.

Cold Water Only Eyewashes

Legionella does not grow favourably in chlorinated water, which is the water supplied to cold water only eyewashes. By flushing eyewash stations frequently with chlorinated water, stagnant water in the dead leg is cleared, and the risk of Legionella growth is minimized. The lower water temperature and the regular application of flushing minimizes the risk of Legionella growth.

Tepid Eyewashes

Tepid eyewashes will be tested in buildings where there has been Legionella found in the laboratory plumbing supply.

4.13 What happens if Legionella was found in a tepid eyewash in a lab?

For red results, the eyewash station will be closed for remediation and undergo cycles of hot water flushing and re-testing until there is a green result. Interim measures will need to be implemented to meet laboratory safety requirements (e.g., a portable eyewash/squeeze bottle for use in the event of an emergency). Interim measures will be reviewed and assessed on a case-by-case basis by EHS. Please contact geoff.shirtliff.hinds@utoronto.ca for a risk assessment.

For orange results, normal operations can continue in the lab, the eyewash is hot water flushed, along with re-testing. For clarity, in the orange category, occupants can continue using the facilities. For more information, please refer to the University’s Water Maintenance Program.

5. Building Maintenance

5.1 Is the water used in the Heating, Ventilation, and Air Conditioning (HVAC) system tested for Legionella?

The domestic water system is separate from the HVAC system. For the HVAC system, there is a chemical used to treat the water to prevent Legionella growth and the concentration of the chemical is monitored in the system at all times.

5.2 My building was last tested in X month, what is next?

EHS is monitoring the situation closely and once testing is completed in a building, the building moves on to the Predictive/Preventative Maintenance Procedure under the University’s Potable Water Maintenance Program.

We continue to encourage JHSCs to provide feedback. University community members are also welcome to review and comment here.