Top 5 Environmental Testers Every Facilities Manager Should Own

5 places you wouldn't expect to find legionella - and how to prevent it.

Monday 28th July 2025

The hot weather has hit the UK as many people start to fill up their hot tubs, turn on their air conditioning units, and head to swimming pools and spas. But legionnaires’ disease can be very serious if handled incorrectly.

What is Legionnaires' disease?

Legionnaire’s disease is a lung infection you can get from inhaling droplets of water from things like air conditioning or hot tubs. It’s uncommon but it can be very serious.

Legionella bacteria, the cause of Legionnaire’s disease, was first discovered in 1976 following an outbreak at a convention of the American Legion in Philadelphia, according to the Centres for Disease Control and Prevention (CDC).

The bacteria was identified as the cause of the pneumonia outbreak, which became known as Legionnaires’ disease.

There were 604 cases of Legionellosis reported to the NELSS in the UK between 2017 to 2023.

What are the symptoms of Legionnaires' disease?

According to the NHS, the below are common symptoms of Legionnaires’ disease:

a cough
shortness of breath
chest pain or discomfort, particularly when breathing or coughing
a high temperature
flu-like symptoms

1. Air conditioning systems

With the warm weather we’ve recently had in the UK, air conditioning units have become a blessing.

Whilst you cannot directly contract Legionnaires’ disease from the air conditioning unit itself, you can from the water in the cooling system if it is not cleaned or maintained properly.

Although It is incredibly rare for domestic air conditioning units found in homes and cars to carry it, commercial buildings, hotels, hospitals, or cruise ships are at an increased risk due to the large, complex HVAC systems that are installed.

These complex systems often use cooling towers that contain warm water. If the water becomes contaminated, this can spread throughout the building when the air conditioning unit is in use, thus leading to the spread of legionella.

How to prevent it: It is essential to undergo regular maintenance checks and should be cleaned regularly in order to prevent the build-up of algae, rust, sludge, and limescale as these provide the perfect conditions for Legionella bacteria to thrive.

2. Humidifiers

Humidifiers have many uses, especially around the home and office. They’re used for relieving dry skin and irritation, easing cold and flu symptoms, and even preventing nosebleeds! Even though the spread of Legionella is extremely rare, adequate care should always be taken to completely avoid it.

Similar to an air conditioning system, humidifiers can become a source of Legionella bacteria if they use standing water and aren’t cleaned regularly.

The warm, stagnant water that is often found in humidifiers creates ideal conditions for Legionella to grow. Cool-mist, ultrasonic, and evaporative humidifiers are particularly at risk if they are not cleaned regularly.

How to prevent it: Using distilled water with a humidifier, emptying, and drying the tank daily can substantially decrease the risk of Legionella bacteria growing, even more so if the unit is thoroughly every week.

3. Hot tubs

Hot tubs have become increasingly popular over the years as they’re more affordable and accessible to households across the UK.

High street stores have made hot tubs easier than ever to purchase, with customers being able to buy and set up the same day.

However, this carries substantial risks, both for the retailer and the consumer. In 2012, two men contracted Legionnaires disease from a warehouse store in Stoke-on-Trent, sparking awareness around Legionella bacteria and hot tubs.

Hot tubs create the perfect environment for Legionella to breed. This is due to the warm water and organic matter that enters the tub on use. If the water is left stagnant for a while, and then reheated, the Legionella bacteria is released into the air as the jets and bubbles agitate the water making it easy to be inhaled.

How to prevent it: The HSE provides a guide on controlling the spread of Legionella, both for commercial and domestic use.

4. Showers

Although the risk remains very low, there has been cases of people catching Legionnaires’ disease from a shower. While it is highly unlikely to catch Legionnaires’ from a home shower, the same can’t be said for the gym, hotel, hospital, or office, this is due to large domestic water systems that are installed and the likelihood of lower water turnover than in the home.

Given the right conditions, Legionella bacteria will grow within the water systems. If the shower is not used for a while, the water will stagnate allowing Legionella to breed. When the shower is turned on, the contaminated water droplets spread via the spray that is produced, causing people to breathe them in.

How to prevent it: The water tank must be inspected regularly and kept clean. A tight-fitting lid is recommended to prevent debris from entering. Using limescale remover also helps to eliminate Legionella bacteria.

5. Garden hoses and watering cans

While this may come as a surprise, garden hoses and watering cans can be a source of Legionella bacteria, especially if they are left stagnant in warm weather.

Legionella thrives in warm conditions and is aerolised when the garden hose is turned on.

A 63 year old man died from Legionnaires’ disease contracted from his garden hose pipe. He developed flu-like systems shortly after using the hosepipe in his garden.

How to prevent it: Ensure hosepipes and watering cans are drained thoroughly before storing them in a cool, shaded place, and avoid using them to fill hot tubs or spa pools. Flush the hosepipe thoroughly before using again.

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