legionella bacteria in hot water system

Can Bacteria Grow in Hot Water Systems?

Now more than ever, we’re concerned with keeping ourselves, our homes and our workplaces clean. Did you know that bacteria can grow in hot water cylinders? This often-overlooked appliance could be putting your family at risk. Don’t fear, Metropolitan Plumbing has everything you need to know about bacteria in hot water systems to keep your family safe.

What Bacteria Can Grow in Water Heaters?

The most common culprit found in domestic hot water systems is Legionella pneumophilia. You will find Legionella in a variety of environments with water or soil, given the right conditions. They live in amoeba, another microbe, and can be inhaled via contaminated water droplets in the air. Once inhaled they can infect cells in your lungs and cause Legionnaires’ Disease or the less severe Pontiac fever.

Thankfully, most Legionella infections only result in Pontiac fever. This is only exhibited as mild flu-like symptoms. It is usually resolved without treatment in 2-5 days.

Legionnaires’ disease, however, is much more serious. Severe pneumonia often accompanies it. In health and nursing home settings, the mortality rate from this disease is as high as 40% according to the Department of Health’s Guidelines for Legionella control. For the immunocompromised, the young and the elderly, it is important they are not exposed to Legionella.

How Do You Kill Bacteria in Hot Water Systems?

Treatment to remove Legionella is already in place before you receive the water. There are steps you can take to minimise the risks as well.

Water Treatment and Transport

Your supplier treats your water supply with a disinfectant before delivering it to you. Chlorine is the most common, but there are several other disinfectants available:

  • Heat
  • Chlorine dioxide
  • Copper-silver ionisation
  • UV light
  • Ozonation
  • Point-of-use microfiltration

Legionella is present in natural water sources before treatment. Some will still remain post-treatment as well. Legionella live in biofilms. These are environments of all different kinds of microbes in a membrane. This shelters some Legionella from the disinfectants and also provides it with nutrients to grow.

Transporting it from the water supply to your home also has the risk of growing bacteria. This depends on the residual disinfectant, temperature and more.

Water Temperature of Hot Water Systems

We enjoy warm water for our showers, and Legionella like this very same warm water to grow and multiply! For hot water systems of the storage tank variety, you need to be especially careful about the temperature of your water. Anywhere between 20-45°C and your water is in the danger zone for Legionella growth. Its most optimal temperature for growth is 37-43°C.

When installing your water heater, your plumber will set the thermostat to heat your water to a minimum of 60°C. This is part of Australian regulations to prevent bacterial growth in your hot water tanks. In 60°C water, 90% of Legionella bacteria will die in 2 minutes. At 70°C, however, they will all die nearly instantly!

Legionella bacteria were still found in many electric water heaters even when the temperature was set to 60°C or above, however. This was due to uneven heating in the tank and so the bottom was only reaching 30-40°C – the sweet spot for Legionella growth. This warm water is not sufficient to keep bacterial growth at bay.

Tempering Valve

Tempering valves are a requirement for hot water systems in Australian residential homes. They are installed at only allow 50°C hot water in fixtures for sanitary plumbing, such as the shower or bathroom sink. Thermostatic mixing valves (TMVs) perform the same job, but are more accurate. Nursing homes, child daycares, and other similar businesses use TMVs for their accurate 50°C hot water.

While 50°C is not in the danger zone, it is not in the optimal water temperature to kill Legionella bacteria. It is vitally important these valves are well maintained and flushed regularly to ensure bacteria doesn’t grow here.

Flush the System

If your plumbing system isn’t set up correctly, there may be regions where water pools and becomes stagnant in your pipes. The temperature of the water is uncontrolled here and might be prone to bacteria growth. Mineral deposits can also build up in your water heater and pipes and affect your water pressure and lead to other plumbing problems

Your plumbing system should be regularly flushed to remove any bacteria and build-up. Better yet, a plumber should repair areas where water stagnates in the first place.

Regular Services

You can have the temperature set correctly to 60°C  and have the system flushed regularly but without regular servicing of hot water systems and general plumbing, there might still be bacteria growth. If the thermostat is faulty, for example, your water isn’t heating as it should. Without the trained eyes of a plumber, who knows how long the temperature will be off the 60°C and allowing bacteria to grow?

Luckily preventing the growth of Legionella bacteria in hot water systems is a pretty simple process. All it takes is ensuring your water heater is working as it should, and regularly having it serviced so it stays this way for the foreseeable future. To find out more about hot water systems from a licensed plumber, contact Metropolitan Plumbing.


Published: 3 Aug, 2020

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