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Five steps to keeping your water system safe from Legionella Bacteria

Legionella during COVID19

As the world returns to work confused and uncertain of the COVID19 🦠 - secure strategies which should be in place to safeguard the staff and visitors in workplaces, a sinister bacteria may be lurking in water systems that have been unused for months. The last thing everyone needs is another outbreak of a different kind of lung disease.

Return to work during COVID19

As many buildings have moved to working from home model, water usage in the buildings has been significantly reduced, and Legionella bacteria may be growing in your water systems. Legionella bacteria can proliferate at temperatures between 20°C and 45°C, where a suitable nutrient is available and where turnover of water is low. As water usage is reduced the risk of low turnover and stagnation increases.

And if you are thinking that there is another complicated guidance coming your way, designed to address those issues, you will be pleased to know that basic management of legionella can be summarised in 5 simple steps:


Ensure that hot water is delivered to all outlets at a minimum of 50°C within 1 minute of flushing (55°C in healthcare). On larger systems that means setting your hot water storage to at least 60°C. Legionella Bacteria is killed at those temperatures. Ensure that all water heaters are switched on, operational and set to the right temperature. Switch on all the pumps and immersion heaters too.

Keep your cold water at a temperature below 20°C. Whether stored in the water tank or supplied directly from mains – cold water should be delivered to all outlets at the temperature below 20°C within 2 minutes of flushing the tap.
But how to do it?
If the water isn’t used, it will gain heat, so make sure you are flushing all your outlets regularly. An initial higher temperature at the outlet is not uncommon, but this reading should drop when the outlets are flushed.

The summer is over now, so the seasonal temperature gain should not be an issue. Any elevated cold water temperatures would most likely be associated with lack of use or design problems that would have to be investigated by a competent person.


Limescale, sediment, corrosion and biofilms are providing nutrients for legionella bacteria. Simply, by keeping your systems clean, you will be reducing the risk of the organism growing in your buildings. Ensure that your water tanks are clean, remove the scale from all outlets, especially showers. Replace or remove corroded elements of your distribution pipework. Once cleaned – keep them clean.


Reduced usage may lead to stagnation, and stagnation will lead to bacterial growth. Make sure that the water turnover on all your systems is sufficient. All outlets should be used at least once a week, and if not- these should be flushed weekly. Ideally, where possible, remove all unused outlets. Check your water tanks for stagnation, address any issues and don’t be afraid to seek advise from a competent person if needed. Avoid dead legs and dead ends – pipework that is no longer serving any outlets or appliances. These provide a perfect environment for bacteria growth. Remove all by cutting them back to live system. Don’t forget about dishwashers, washing machines, drinking water dispensers, showers, outside taps – all require flushing or removal.


The above advice is not site specific, and your building may be a little bit more complicated. Those four steps are forming the most basic legionella control plan, which should already be in place in your building. This step requires a documentation and written scheme review: make sure that you have an up to date risk assessment, ensure that all PPM tasks are being completed and perform an audit of all records. Implement changes where required.

Most of all do not panic, keep calm and reach out if you need help with your legionella management.

Stay Safe

Yours Sincerely

The First Principle Group Team

PS. Feel free to schedule a no-obligation chat with our friendly consultant

Legionella during COVID19

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