Legionella FAQ
Answers to Common Questions About Legionnaires’ Disease and Cooling Tower Safety in Victoria
This Legionella FAQ brings together the most common questions we’re asked about Legionella bacteria, Legionnaires’ disease, and how to keep your site compliant under Victorian law.
If you operate a cooling tower system, you already play a key role in protecting building occupants and the wider community from Legionella. The Public Health and Wellbeing Regulations 2019 (Vic) require strict control, monitoring, and record-keeping to prevent outbreaks, but the details can sometimes feel complex.
At Tandex, our goal is to simplify this process. We help clients understand their responsibilities, keep their cooling towers in top condition, and maintain compliance confidence year-round, which is why many sites rely on Tandex as their long-term water treatment partner. If you haven’t already, you might like to read our Understanding Legionella and Legionnaires’ Disease article for a deeper background before diving into these FAQs.
Legionella are naturally occurring bacteria that multiply in warm, stagnant water, especially in systems where biofilm, scale or sludge accumulate. In the right environment, these bacteria multiply rapidly and can become airborne through tiny droplets of water (aerosols).
They’re commonly found in cooling towers, warm water systems, spas, and decorative fountains. In Victoria, cooling towers are regulated under the Public Health and Wellbeing Regulations 2019, which require all towers to be registered and maintained under a Risk Management Plan (RMP).
At Tandex, we help building owners manage these risks through our Cooling Tower Services. Our services ensure every system is maintained, tested, and documented in full compliance with Victorian standards.
For further information on Legionella and Legionnaires’ disease, refer to the Victorian Department of Health.
Legionnaires’ disease is caused when people inhale fine water droplets that contain Legionella bacteria. These droplets are typically released from mist-producing systems such as cooling towers, showers, spa pools, or decorative fountains.
It is important to note that Legionnaires’ disease is not contagious and does not spread from person to person. Most outbreaks occur when poorly maintained water systems allow bacteria to multiply and disperse into the air through drift or mist.
Our Understanding Legionella and Legionnaires’ Disease post explains this process in more depth and explores the conditions that allow the bacteria to grow, including temperature and stagnation.
Anyone can become infected, but the risk is highest for:
- Adults over 50 years of age
- Smokers or people with chronic respiratory disease
- Individuals with weakened immune systems or serious health conditions
While most healthy people recover fully, the illness can be severe or even life-threatening for vulnerable groups. That’s why preventing Legionella growth in building water systems is so important.
Managing cooling towers or other regulated systems carries a legal duty under Victorian law to minimise exposure risk. Tandex provides tailored maintenance and testing programs to help you meet those obligations with confidence.
- Warm water systems with poor temperature control
- Spa pools and hydrotherapy baths
- Decorative fountains and water features
- Potting mix and soil, which can harbour a related species, Legionella longbeachae
Because Legionella can develop in multiple water systems, prevention relies on regular cleaning, monitoring, and good design. For information about how cooling tower maintenance prevents contamination, visit our Cooling Tower Services page.
You do not need a positive test result to suspect something is wrong, as many visual or operational signs can indicate elevated risk:
- Slime, algae, or biofilm inside the tower basin
- Cloudy water or a musty odour
- Rust, scale, or sediment accumulation
- Stagnant water or low circulation
- Drift eliminators that are missing or damaged
If your system shows these signs, it’s worth arranging a review before your next scheduled test, as unresolved system issues can quickly lead to operational disruptions and unplanned cooling tower downtime.
Tandex technicians check these indicators as part of every service visit, helping our clients identify issues early and maintain safe conditions between formal Legionella tests.
Department of Health: Cooling tower maintenance and testing guidance.
- Sampled and tested for HCC monthly
- Sampled and tested for Legionella at least every three months (the exact frequency is dictated by the risk posed by the system as per the RMP)
- Inspected monthly to verify that chemical dosing and control equipment are functioning correctly
Additional testing is required whenever DHHS dictates, and regular testing not only demonstrates compliance but also helps detect emerging issues before they escalate.
Tandex manages the full Legionella testing process for clients, including sample collection, laboratory coordination, and result interpretation. You can learn more about our monthly programs on our Cooling Tower Services page.
Read more at Victorian Department of Health: Regulatory framework for Legionella.
- Public Health and Wellbeing Act 2008 (Vic)
- Public Health and Wellbeing Regulations 2019 (Vic)
- AS/NZS 3666.1–3 – Air-handling and water systems of buildings
- Department of Health: Guidelines for the Control of Legionella in Regulated Systems
Together, these outline how cooling towers must be registered, cleaned, disinfected, and tested.
For an overview of the legislation and its practical requirements, see our Compliance page. Tandex helps ensure every site meets these standards, with recordkeeping, RMP development, and documentation ready for audit.
- Registering all cooling towers with the State Government and renewing the registration when due
- Maintaining a current Risk Management Plan (RMP), including completing a formal review annually
- Have an approved auditor complete annual audits of the RMP and treatment program
- Notify the appropriate Health Authority immediately of any changes to the site, contact details, responsible persons, or system
- Contracting a water treatment provider to conduct services, inspections, and testing in line with the program defined in the RMP
- This includes ensuring the system is continuously treated with one or more biocides, corrosion and scale inhibitors, and biodispersants
- Contracting a water treatment provider to perform regular cleaning and disinfection of the system in line with the program defined in the RMP
- Including disinfection and cleaning of the system following any period of shutdown that exceeds one month
- Keeping complete records of maintenance and test results
- Notifying the appropriate Health Authority within 24 hours when Legionella is detected in three consecutive samples from the system or at a level greater than 1,000 CFU/mL
These responsibilities are set out under the Public Health and Wellbeing Regulations 2019 (Vic). Our team assists clients in understanding and meeting every part of these obligations. To see how, visit our Compliance page.
- Legionella and HCC test results
- Cleaning and disinfection records
- Maintenance logs and corrective actions
- RMP audits and updates
These records form the foundation of a defensible compliance position. Tandex issues comprehensive documentation following every service and test, supporting clients in meeting audit requirements with confidence.
- <10 CFU/mL: Satisfactory result – considered negative for Legionella
- >10 CFU/mL: Unsatisfactory result – considered positive for Legionella and requires follow-up in accordance with the site’s Risk Management Plan (RMP) and regulatory requirements.
Test results are provided by the laboratory directly to the responsible person managing the testing program, most often the appointed water treatment provider. The water treatment provider then advises the responsible person nominated for the cooling tower system. The resultant report must be kept with the site’s RMP documentation. Further actions are required should a positive result be returned from testing.
Routine testing frequency and result reporting are set out in the site’s RMP and must align with Victorian regulatory requirements for Legionella and Heterotrophic Colony Count (HCC) testing.
- <10 CFU/mL: Satisfactory result, no remedial action required
- 10–1,000 CFU/mL: Remedial action required within 24 hours
- >1000 CFU/mL: Notification to DHHS by the persons responsible for the tower, and remedial action required within 24 hours
For an initial positive Legionella result, the responsible person must ensure these required remedial actions are completed:
- Disinfect the system within 24 hours of receiving the result.
- Review the operation and maintenance program, including chemical dosing, temperature control, and mechanical components.
- Correct any identified faults or deficiencies.
After the disinfection, a follow-up sample must be taken within 2–7 days for further Legionella testing. If this follow-up result is also positive, the system must be cleaned and disinfected within 24 hours, and then resampled again 2–7 days later.
This process must continue until two consecutive samples (typically about a week apart) return negative Legionella results.
The responsible person must notify the relevant health authority in writing if:
- A result exceeds 1,000 CFU/mL, or
- Three consecutive positive Legionella results are received, despite the remedial actions taken.
High Heterotrophic Colony Count (HCC) results can also indicate poor water quality or ineffective biocide control, even when Legionella counts are low. If your site receives any concerning results, Tandex can coordinate the full response: disinfecting and cleaning, arranging follow-up testing, and assisting with updates to your Risk Management Plan (RMP) to prevent recurrence.
If multiple cases of Legionnaires’ disease are linked to a specific area, the Victorian Department of Health (or a local public-health unit) will typically trigger an outbreak investigation focused on potential sources such as cooling tower systems. The investigation process may include:
- Site visits to properties hosting registered cooling towers
- Detailed environmental sampling of water and air systems
- A review of the site’s Risk Management Plan (RMP), maintenance records, testing results, and registration documentation
Importantly, under the Public Health and Wellbeing Act 2008 (Vic), authorised officers have broad powers to inspect and act where there is a risk to public health. They can, for example:
- Enter premises without a warrant when they reasonably believe there is an immediate risk
- Require documents, seize items, and inspect or sample equipment
- Issue directions or take regulatory action if a system is suspected of being the source of an outbreak and cannot produce proof of compliance (registration, RMP, audit records)
While the Act does not always refer specifically to a “shutdown order”, the same regulatory framework gives authorities the power to close or restrict the use of premises if the risk to public health is sufficiently serious.
For site owners and operators, having complete, current and readily accessible documentation (registration certificate, RMP, audit reports, testing records, maintenance logs) is one of the most effective ways to reduce disruption during an investigation. Our Cooling Tower Services are structured to ensure that every client’s records are ready for immediate inspection if required.
- Hot water ≥60 °C, cold water ≤20 °C
- Maintaining biocide residuals within specification
- Regular cleaning and disinfection (at least twice a year)
- Inspecting drift eliminators for damage or blockage
- Maintaining continuous circulation to avoid stagnation
Following these controls keeps systems safe between monthly test cycles. More detail on cooling tower control and maintenance can be found in AS/NZS 3666.2: Operation and Maintenance of Air-handling and Water Systems.
Ignoring your obligations can lead to serious consequences. Penalties under the Public Health and Wellbeing Act 2008 (Vic) can include fines, improvement notices, or enforced system shutdowns. Beyond the legal risk, non-compliance can also cause reputational damage and loss of client confidence if your site is linked to an outbreak.
Tandex helps prevent these outcomes through ongoing maintenance, testing, and compliance documentation, ensuring systems remain audit-ready and operational year-round.
Tandex provides a complete range of Legionella management services, including:
- Routine service, inspections, and Legionella and HCC testing
- Risk Management Plan development and review
- Coordination of annual RMP Reviews and Audits
- Cooling tower cleaning and disinfection coordination
- Compliance documentation and reporting
With decades of industry experience, our team helps clients simplify compliance while protecting health and safety. You can learn more about our services on our Cooling Tower Services or Compliance pages.
Legionella are naturally occurring bacteria that multiply in warm, stagnant water, especially in systems where biofilm, scale or sludge accumulate. In the right environment, these bacteria multiply rapidly and can become airborne through tiny droplets of water (aerosols).
They’re commonly found in cooling towers, warm water systems, spas, and decorative fountains. In Victoria, cooling towers are regulated under the Public Health and Wellbeing Regulations 2019, which require all towers to be registered and maintained under a Risk Management Plan (RMP).
At Tandex, we help building owners manage these risks through our Cooling Tower Services. Our services ensure every system is maintained, tested, and documented in full compliance with Victorian standards.
For further information on Legionella and Legionnaires’ disease, refer to the Victorian Department of Health.
It is important to note that Legionnaires’ disease is not contagious and does not spread from person to person. Most outbreaks occur when poorly maintained water systems allow bacteria to multiply and disperse into the air through drift or mist.
Our Understanding Legionella and Legionnaires’ Disease post explains this process in more depth and explores the conditions that allow the bacteria to grow, including temperature and stagnation.
- Adults over 50 years of age
- Smokers or people with chronic respiratory disease
- Individuals with weakened immune systems or serious health conditions
While most healthy people recover fully, the illness can be severe or even life-threatening for vulnerable groups. That’s why preventing Legionella growth in building water systems is so important.
Managing cooling towers or other regulated systems carries a legal duty under Victorian law to minimise exposure risk. Tandex provides tailored maintenance and testing programs to help you meet those obligations with confidence.
Other potential sources include:
- Warm water systems with poor temperature control
- Spa pools and hydrotherapy baths
- Decorative fountains and water features
- Potting mix and soil, which can harbour a related species, Legionella longbeachae
Because Legionella can develop in multiple water systems, prevention relies on regular cleaning, monitoring, and good design. For information about how cooling tower maintenance prevents contamination, visit our Cooling Tower Services page.
You do not need a positive test result to suspect something is wrong, as many visual or operational signs can indicate elevated risk:
- Slime, algae, or biofilm inside the tower basin
- Cloudy water or a musty odour
- Rust, scale, or sediment accumulation
- Stagnant water or low circulation
- Drift eliminators that are missing or damaged
If your system shows these signs, it’s worth arranging a review before your next scheduled test, as unresolved system issues can quickly lead to operational disruptions and unplanned cooling tower downtime.
Tandex technicians check these indicators as part of every service visit, helping our clients identify issues early and maintain safe conditions between formal Legionella tests.
Department of Health: Cooling tower maintenance and testing guidance.
- Sampled and tested for HCC monthly
- Sampled and tested for Legionella at least every three months (the exact frequency is dictated by the risk posed by the system as per the RMP)
- Inspected monthly to verify that chemical dosing and control equipment are functioning correctly
Additional testing is required whenever DHHS dictates, and regular testing not only demonstrates compliance but also helps detect emerging issues before they escalate.
Tandex manages the full Legionella testing process for clients, including sample collection, laboratory coordination, and result interpretation. You can learn more about our monthly programs on our Cooling Tower Services page.
Read more at Victorian Department of Health: Regulatory framework for Legionella.
- Public Health and Wellbeing Act 2008 (Vic)
- Public Health and Wellbeing Regulations 2019 (Vic)
- AS/NZS 3666.1–3 – Air-handling and water systems of buildings
- Department of Health: Guidelines for the Control of Legionella in Regulated Systems
Together, these outline how cooling towers must be registered, cleaned, disinfected, and tested.
For an overview of the legislation and its practical requirements, see our Compliance page. Tandex helps ensure every site meets these standards, with recordkeeping, RMP development, and documentation ready for audit.
- Registering all cooling towers with the State Government and renewing the registration when due
- Maintaining a current Risk Management Plan (RMP), including completing a formal review annually
- Have an approved auditor complete annual audits of the RMP and treatment program
- Notify the appropriate Health Authority immediately of any changes to the site, contact details, responsible persons, or system
- Contracting a water treatment provider to conduct services, inspections, and testing in line with the program defined in the RMP
- This includes ensuring the system is continuously treated with one or more biocides, corrosion and scale inhibitors, and biodispersants
- Contracting a water treatment provider to perform regular cleaning and disinfection of the system in line with the program defined in the RMP
- Including disinfection and cleaning of the system following any period of shutdown that exceeds one month
- Keeping complete records of maintenance and test results
- Notifying the appropriate Health Authority within 24 hours when Legionella is detected in three consecutive samples from the system or at a level greater than 1,000 CFU/mL
These responsibilities are set out under the Public Health and Wellbeing Regulations 2019 (Vic). Our team assists clients in understanding and meeting every part of these obligations. To see how, visit our Compliance page.
- Legionella and HCC test results
- Cleaning and disinfection records
- Maintenance logs and corrective actions
- RMP audits and updates
These records form the foundation of a defensible compliance position. Tandex issues comprehensive documentation following every service and test, supporting clients in meeting audit requirements with confidence.
- <10 CFU/mL: Satisfactory result – considered negative for Legionella
- >10 CFU/mL: Unsatisfactory result — considered positive for Legionella and requires follow-up in accordance with the site’s Risk Management Plan (RMP) and regulatory requirements.
Laboratories provide these results directly to the responsible person responsible for facilitating the testing – usually the water treatment provider. The water treatment provider then advise the responsible person nominated for the cooling tower system. The resultant report must kept with the site’s RMP documentation. Further actions are required should a positive result be returned from testing.
Routine testing frequency and result reporting are set out in the site’s RMP and must align with Victorian regulatory requirements for Legionella and Heterotrophic Colony Count (HCC) testing.
- <10 CFU/mL: Satisfactory result, no remedial action required
- 10–1,000 CFU/mL: Remedial action required within 24 hours
- >1000 CFU/mL: Notification to DHHS by the persons responsible for the tower, and remedial action required within 24 hours
For an initial positive Legionella result, the responsible person must ensure these required remedial actions are completed:
- Disinfect the system within 24 hours of receiving the result.
- Review the operation and maintenance program, including chemical dosing, temperature control, and mechanical components.
- Correct any identified faults or deficiencies.
After the disinfection, a follow-up sample must be taken within 2–7 days for further Legionella testing. If this follow-up result is also positive, the system must be cleaned and disinfected within 24 hours, and then resampled again 2–7 days later.
This process must continue until two consecutive samples (typically about a week apart) return negative Legionella results.
The responsible person must notify the relevant health authority in writing if:
- A result exceeds 1,000 CFU/mL, or
- Three consecutive positive Legionella results are received, despite the remedial actions taken.
High Heterotrophic Colony Count (HCC) results can also indicate poor water quality or ineffective biocide control, even when Legionella counts are low. If your site receives any concerning results, Tandex can coordinate the full response: disinfecting and cleaning, arranging follow-up testing, and assisting with updates to your Risk Management Plan (RMP) to prevent recurrence.
- Site visits to properties hosting registered cooling towers
- Detailed environmental sampling of water and air systems
- A review of the site’s Risk Management Plan (RMP), maintenance records, testing results, and registration documentation
Importantly, under the Public Health and Wellbeing Act 2008 (Vic), authorised officers have broad powers to inspect and act where there is a risk to public health. They can, for example:
- Enter premises without a warrant when they reasonably believe there is an immediate risk
- Require documents, seize items, and inspect or sample equipment
- Issue directions or take regulatory action if a system is suspected of being the source of an outbreak and cannot produce proof of compliance (registration, RMP, audit records)
While the Act does not always refer specifically to a “shutdown order”, the same regulatory framework gives authorities the power to close or restrict the use of premises if the risk to public health is sufficiently serious.
For site owners and operators, having complete, current and readily accessible documentation (registration certificate, RMP, audit reports, testing records, maintenance logs) is one of the most effective ways to reduce disruption during an investigation. Our Cooling Tower Services are structured to ensure that every client’s records are ready for immediate inspection if required.
- Hot water ≥60 °C, cold water ≤20 °C
- Maintaining biocide residuals within specification
- Regular cleaning and disinfection (at least twice a year)
- Inspecting drift eliminators for damage or blockage
- Maintaining continuous circulation to avoid stagnation
Following these controls keeps systems safe between monthly test cycles. More detail on cooling tower control and maintenance can be found in AS/NZS 3666.2: Operation and Maintenance of Air-handling and Water Systems.
Tandex helps prevent these outcomes through ongoing maintenance, testing, and compliance documentation, ensuring systems remain audit-ready and operational year-round.
- Routine service, inspections, and Legionella and HCC testing
- Risk Management Plan development and review
- Coordination of annual RMP Reviews and Audits
- Cooling tower cleaning and disinfection coordination
- Compliance documentation and reporting
With decades of industry experience, our team helps clients simplify compliance while protecting health and safety. You can learn more about our services on our Cooling Tower Services or Compliance pages.
Protect your people, your property, and your reputation with professional Legionella testing and compliance support from Tandex.
Stay compliant, protect your occupants, and prevent outbreaks with professional Legionella testing and risk management from Tandex.
