Department of Health

The guidance information includes an abbreviations list, a glossary and a bibliography.


CFU: colony forming units

CTS number: cooling tower system number

the department: the Victorian Department of Health

HCC: heterotrophic colony count

RMP: risk management plan


  • A place where acute health care is provided (such as a hospital) or aged residential care facilities (such as nursing homes or hostels).

  • A system comprising:

    • a cooling tower or a number of interconnected cooling towers that use the same recirculating water
    • any machinery that is used to operate the tower(s)
    • any associated tanks, pipes, valves, pumps or controls.
  • A process used when a cooling tower system is suspected or implicated as a source of Legionnaires’ disease. The decontamination process is usually determined in consultation with the Department of Health Legionella Team. It involves a series of actions to disinfect, clean and re-disinfect the cooling tower system (see Appendix 9).

  • A process intended to kill or remove pathogenic microorganisms, including Legionella.

    In the case of a cooling tower system, disinfection consists of dosing the water of a system with either:

    • a chlorine-based compound, equivalent to at least 10 mg/L of free chlorine for at least 1 hour, while maintaining the pH of the water between 7.0 and 7.6; or
    • a bromine-based compound, equivalent to at least 20 mg/L of free bromine for at least 1 hour, while maintaining the pH of the water between 7.0 and 8.5.
  • An estimate of the number of viable units of bacteria per millilitre of water made using the pour plate, spread plate or membrane filter test. Also known as total bacteria count, total plate count or viable bacteria count test.

  • Owner in relation to the land or Crown land within the meaning of the Public Health and Wellbeing Act 2008.

  • Person who owns, manages or controls the cooling tower system.

  • The frequency with which the cooling tower system is thoroughly checked by a competent person. It includes a check of the water quality, as well as physical components.

  • The manual addition, in a single dose, of a much higher amount of chemical biocide than is normally applied, with the intention of rapidly raising the concentration of biocide in the water to a level expected to kill most if not all organisms in the water.

  • A device that automatically discharges a measured amount of chemical to the water inside a cooling tower system.

  • A physical or chemical agent capable of killing microorganisms, including Legionella bacteria.

  • A chemical added to the water inside a cooling tower system, to penetrate and break down any biofilm that may be present on the wetted surfaces.

  • A surface layer of microorganisms. It is usually combined with particulate matter, scale and products of corrosion.

  • Colony forming units per millilitre. The unit of measure of bacterial levels in a sample.

  • Cleaning if a cooling tower system involves the following steps:

    1. Thoroughly clean the internal shell, fill and tower sump by brushing and/or hosing all surfaces.
    2. Remove all debris.
    3. Thoroughly clean internally and externally all water filters, strainers, separators, water nozzles and fittings associated with the water distribution system.
  • A device for lowering:

    • the temperature of recirculated water, by bringing the water into contact with fan-forced or fan-induced atmospheric air; or
    • the temperature of water, a refrigerant or other fluid in a pipe or other container, by bringing recirculated water and fan-forced or fan-induced atmospheric air into contact with the pipe or container.

    An evaporative air cooler or evaporative air-conditioner is not a cooling tower.

  • A structure at the top of a cooling tower that is designed to create an extensive wetted surface area through which air passes.


Australian Standards:

  • AS/NZS 3666: Air-handling and water systems of buildings – Microbial control
  • AS/NZS 3666.1: Air-handling and water systems of buildings – Microbial control – Design, installation and commissioning
  • AS/NZS 3666.2: Air-handling and water systems of buildings – Microbial control – Operation and maintenance
  • AS/NZS 3666.3: Air-handling and water systems of buildings – Microbial control – Performance-based maintenance of cooling water systems
  • AS 4276.3.1: Water microbiology – Heterotrophic colony count methods – Pour plate method using yeast extract agar
  • AS/NZS 3896: Waters – examination for Legionella spp. including Legionella pneumophila
  • AS 2031-2012: Water quality – Sampling for microbiological analysis
  • AS/NZS 1715: Selection, use and maintenance of respiratory protective equipment
  • AS/NZS 1716: Respiratory protective devices
  • AS/NZS 1336: Eye and face protection – Guidelines
  • AS/NZS 1337.1/Amdt 1: Personal eye protection – Eye and face protectors for occupational applications
  • AS/NZS ISO 31000: Risk management – Principles and guidelines.

Australian Institute of Refrigeration, Air Conditioning and Heating. Design Application manuals DA17: Cooling towers and DA18: Water treatment.

Reviewed 20 December 2021


Contact details

Our phone service is available Monday to Friday, from 9.00am to 1.00pm. Postal address: GPO Box 4057, Melbourne Vic 3001

Legionella team

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