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Determining if a heated water system is captured under the Legionella Regulations

Due to the age, design and modification of some heated water systems, it can be difficult to determine if they are warm water systems that are captured under the South Australian Public Health (Legionella) Regulations 2013.

The following has been designed to assist you in determining if a heated water system is captured. 

Warm water systems – why are they a risk

Warm water provides the ideal temperature for the growth of Legionella bacteria, the causative agent of Legionnaires’ disease.

When water containing Legionella is aerosolised through processes such as showering, there is a risk that it can be inhaled and Legionnaires’ disease can result. The risk from Legionella can be managed through the proper design, installation, operation and maintenance of heated water systems.

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Systems that deliver warm water

There are two main system designs that result in the automatic delivery of warm water:

  • Systems that distribute or recirculate warm water throughout the majority of the system by means of a temperature controlling device or devices, usually located close to the hot water storage tank or water heating device(s). These are often referred to as tepid or tempered warm water systems
  • Systems that deliver hot water 60oC or more to automatic temperature controlling devices (such as thermostatic mixing valves) where it is cooled to the desired temperature by mixing with cold water, prior to delivery at the outlet(s). The mixing valves are located close to the outlets (ideally maximum six metres of pipe from valve to outlet).

All systems that deliver warm water are capable of growing Legionella, and may potentially cause Legionnaires’ disease.

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Tepid warm water systems

All tepid warm water systems are captured by the Legionella Regulations.

Tepid warm water systems distribute or recirculate warm water through the majority of the system at temperatures conducive to the growth of Legionella (nominally 45oC).

If colonised with Legionella, these types of systems usually present a health risk to a greater number of people than systems which mix hot and cold water using temperature controlling devices located close to the outlets.

Tepid warm water systems are depicted in Figures 5 and 6 of Schedule 1 of the Legionella Guidelines (PDF 270KB).

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Heated water systems incorporating thermostatic mixing valves (TMVs)

TMVs may be contained in both warm and hot water systems. Only warm water systems are captured by the Legionella Regulations.

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Hot water systems incorporating TMVs

The Legionella risk associated with hot water systems incorporating TMVs may be reduced if the TMVs are located in close proximity to the outlet(s) they serve, resulting in the presence of hot water 60oC or less through the majority of the system. To minimise water stagnation, heat loss and the growth of microorganisms, including Legionella, it is recommended that the length of pipe work from a TMV to each of its outlets does not exceed six metres.

These systems are not risk free, and Legionella bacteria is commonly isolated from such systems. Hot water systems are depicted in Figures 3 and 4 of Schedule 1 of the Legionella Guidelines (PDF 270KB).

Hot water systems with TMVs located 6 meters or less from outlets are not captured by the Legionella Regulations

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Hybrid systems

Some systems, originally designed as hot water systems, may have been extensively modified, resulting in the system no longer bearing any resemblance to its original design. Such a system can be described as a hybrid system. Hybrid systems are often complex in their design and commonly lack accurate plans.

The modification of a hot water system will not necessarily result in the system automatically being deemed to be a warm water system and vice versa. Plans for modifications should be assessed by the relevant authority to determine whether the regulated status of the system will change.

Hybrid systems must be thoroughly assessed to determine whether they are captured by the Legionella Regulations.

It is important to note that all systems that automatically deliver warm water are capable of growing Legionella and may potentially cause Legionnaires’ disease.

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Help assessing the system

If there is any uncertainty about the regulated status of a heated water system, the system should be assessed by an environmental health officer from the local council. You must provide plans or a scale sketch of the system that identifies:

  • the location of the water heater(s) and/or hot water storage unit(s)
  • all temperature controlling devices (TMVs or tempering valves)
  • the temperature of the water (hot, cold or warm)
  • plans of pipework indicating the direction of flow of the water

Some facilities, premises and institutions may have multiple discreet systems. Each separate system must be assessed as an individual entity.

Changes to a heated water system, such as the relocation of valves or the addition of new pipe work, may change the regulated status of the system. The system must be re-assessed when any such modifications are made.

If a small mixing valve system technically meets the definition of a warm water system, but the pipe lengths from each mixing valve to all outlets do not exceed six metres (for example, it is equivalent to the warm sections of a well-designed hot / TMV system), the system may be deemed to be a hot water system by the relevant authority (not captured by the Legionella Regulations).

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Still not sure

If you are unable to reach a conclusion on the regulated status of a system, contact SA Health’s Health Protection Programs on (08) 8226 7100 or email healthprotectionprograms@health.sa.gov.au for further advice.

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