Judging by the number of phone calls in the last few days to Whywait Plumbing there is genuine concern amongst our clients over the threats posed to them from Legionella risk in their domestic hot water systems.

legionella risk from hot waterWe can assure you whilst there is always some Legionella risk, there is almost no risk of you or your family contracting Legionella bacteria as a result of it breeding in your home hot water system.

The outbreak of Legionella bacteria in the hot water system at Wesley Hospital that killed a 60-year-old cancer patient and left a 46-year-old woman seriously ill has minor ramifications to be sure because all hot water systems can pose a risk.

That potential risk is why Whywait Plumbing is constantly advocating appropriate maintenance on your home hot water system to minimise that risk even further.

However, there is a huge difference between your home or domestic hot water system and the warm water recirculating system at Wesley Hospital. The Legionella outbreak in their warm water system has not been as a result of contamination in the hot water storage system or the hot water pipes but appears to be literally at the point of delivery from the shower where the water is cooler.

A warm water system is vastly different to your home hot water system with Wesley’s water temperature set between 42.5°C and 43°C. This is lower than the maximum 45°C legislated in the Plumbing and Drainage Act for hospitals. This low-temperature setting is a result of guidelines from Queensland Health that dictate hot water temperatures in hospitals be reduced to avoid the possibility of serious burns to young children and elderly patients. The downside of this requirement is that the possibility of Legionella bacteria surviving in reticulation pipes is increased. Water temperatures of around 46°C will kill legionella bacteria.

Warm water systems are typically found in care facilities, such as nursing homes, hospitals and child care centres, where water for purposes such as bathing and cleaning is provided at approximately 45°C to prevent scalding.

Your home hot water system if it is a storage tank is heating the hot water to between 60°C and 70°C. If you have a tempering valve or thermostatic mixing valve (TMV) installed then that has been set to deliver hot water at 50°C at each individual tap.

legionella risk reduced with TMVIf you have no tempering valve installed, you virtually have eliminated all risk. But you have increased the risk of someone suffering a scalding from hot water. As always it is about managing risk.

However, there is an urban myth prevalent that you can reduce electricity costs by turning the thermostat down on an electric storage unit to 50°C. This is not recommended for many reasons but it will not save you electricity and to physically get a thermostat down that low requires physically breaking the locking mechanism on it that allows the setting to be between 60°C – 70°C. If you want to lower the delivery temperature the only acceptable and compliant method is to install a tempering valve.

In 99.99% of cases, the temperature ranges your hot water system operates in is almost certainly killing any Legionella bacteria. The risk if any, is after the storage tank in the reticulation pipes. By turning your shower on and running the tap with hot water first then cooling down with cold water to your desired shower temperature you are virtually eliminating what risk there is.

What the outbreak at Wesley Hospital has confirmed is that there is a risk from warm water and that maintenance of your hot water systems will manage and eliminate that risk.

What Whywait Plumbing do recommend is that you take advantage of our ongoing reminders and offers to service your tempering valves. This not only ensures that water is being delivered at 50°C but eliminates any possibility of Legionella. It also ensures you are complying with the requirements of most insurance policies in ensuring that routine maintenance is undertaken plus we provide you with a written report and a form 4 compliance certificate that is further evidence of your hot water unit being compliant.

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