Potable water tanks are a fantastic option for storing safe drinking water if access to mains water is not an option. Whilst potable water tanks provide an efficient way to access water they can also pose a significant health risk if not strictly maintained.
Over time potable water tanks can become dirty with debris, sediment and other contaminants, providing the perfect breeding ground for harmful bacteria such as Legionella. Legionella in water can cause serious health conditions in certain groups including those over the age of 45, smokers and those with weakened immune systems. As an employer or premise manager, it is your duty to follow the Legionella Regulations.
But what is Legionella, and how do you prevent Legionella in water tanks? In this article, we will explore what Legionella is and the steps you can take to mitigate the risk of it infecting your potable water tanks.
What causes Legionella in cold water tanks?
How long does legionella take to develop in water?
What temperature does Legionella grow?
What temperature kills Legionella?
What are the UK’s Legionella regulations?
How to carry out a Legionella risk assessment
How to test for Legionella in water
How can I prevent Legionella in cold water tanks?
What is Legionella?
Legionella is a bacteria that is commonly found in natural aquatic environments. Exposure to the Legionellales bacteria can put you at risk of Legionnaires’ disease, which is a serious type of pneumonia that can prove fatal to some individuals.
What causes Legionella in cold water tanks?
The Legionella bacteria thrive in warm, damp environments making purpose-built water storage systems such as potable water tanks the ideal environment for growth. Several factors can encourage the growth of Legionella in cold water storage tanks which we will explore below.
Storage temperature
One of the primary factors that lead to Legionella growth in cold water tanks is inadequate storage temperature. Between 20°C and 40°C, legionella can multiply, rapidly infecting the entire water system.
Stagnant water
Stagnant water allows biofilms to develop and grow, which can provide a food source for the Legionella bacteria. Biofilms can also protect the Legionella bacteria from disinfectants, making the bacteria harder to eradicate.
Inadequate storage tank
For potable water, it must be stored in a tank approved under the Water Regulations Approval Scheme (WRAS). WRAS-approved water tanks are made from food-grade polyethene and well fitting lids, protecting the water from external contaminants and extreme weather conditions. If a storage tank is inadequate or faulty, it can put the water at risk of contamination.
How long does legionella take to develop in water?
If the correct precautions have not been followed, Legionella can develop in as little as a few days to a couple of weeks. Once the bacteria has started to grow, it will multiply quickly, infecting the entire water system if left untreated.
What temperature does Legionella grow?
Legionella bacteria thrive in temperatures between 20°C and 45°C. Outside of these temperatures, the bacteria will struggle to survive.
What temperature kills Legionella?
To effectively kill Legionella bacteria, the water temperature should be below 20°C or above 50°C. The speed at which the bacteria dies increases as the water temperature increases, as shown in the table below.
|
Water temperature |
Effect on Legionella bacteria |
|
<20°C |
Legionella bacteria can survive but remain in a dormant state |
|
20-40°C |
Legionella bacteria can thrive and reproduce rapidly infesting entire water systems |
|
50°C |
90% of Legionella bacteria die off within two hours |
|
60°C |
90% of Legionella bacteria die off within 2 minutes |
|
70°C |
Legionella bacteria die instantly |
What are the UK’s Legionella regulations?
In the UK, it is the responsibility of the building owner to follow the relevant legislation to mitigate the chances of contamination. As the person responsible, there are a few Legionella regulations that you should be aware of, including
- Health and Safety at Work Act 1974
- The Control of Substances Hazardous to Health Regulations 2002 (COSHH)
- Management of Health and Safety at Work
How to carry out a Legionella risk assessment
In the UK there is a legal requirement for any duty holder to conduct a legionella risk assessment as detailed under the Health and Safety at Work Act 1974, Management of Health and Safety at Work and COSHH.
Legionella risk assessments are intended to identify potential risks to both employees and customers. It is recommended that these risk assessments are done annually and the exact steps needed will vary depending on the size and type of water system being used. Generally, a Legionella risk assessment will involve:
- Identifying any potential hazards
- Identifying who is at risk
- Testing the water system (although this is not a legal requirement, this is often carried out as part of a professional risk assessment)
- Putting measurements in place to reduce the risk
- Recording the outcome of the assessment and generating remedial actions with different severities and timescales
How to test for Legionella in water
Whilst testing or sampling for Legionella is not legally required, it is good practice to do so alongside an annual risk assessment. There are various tests available for testing for Legionella, and the type you need will depend on the water system you have.
In most cases, it will involve taking a water sample in a sterilised container which would then be sent on to a laboratory for testing. There are also testing kits that allow you to test on-site and work similarly to a Litmus test.
How can I prevent Legionella in cold water tanks?
The risk of Legionella is preventable and there are several steps you can take to avoid legionella growth in your cold water tanks.
Ensure the water tank is WRAS-approved
WRAS-approved tanks are made from food-grade polyethylene which is a durable plastic. The smooth interior walls of the tanks restrict bacteria growth and allow for easy cleaning, whilst the UV-stabilised materials protect the water from extreme weather conditions.
Eliminate dead legs
Dead legs refer to any sections of piping that are no longer used. This piping can allow for stagnant water to collect, creating an ideal environment for Legionella to form. It is recommended that a dead leg should be no longer than twice the width of your pipe.
Use an appropriate-sized potable water tank
As Legionella can thrive in stagnated water you must choose an appropriate-sized water tank to ensure the water does not sit stagnant for extended periods. The right-sized tank will mean that water is regularly replenished. At Kingfisher Direct, we supply suitable water tanks as small as 5-200 litres and potable water tanks up to 30,000 litres.
Regular monitoring and risk assessments
Potable water tanks should be routinely cleaned and inspected to ensure that they meet the requirements for safe drinking water. Continuous monitoring will allow you to identify any risks before they arise and put plans in place to avoid bacteria growth.
Providing that the water is stored correctly and is regularly monitored, drinking water can remain safe for several months. That being said, it is always advised to replenish the water frequently to avoid the water becoming stagnant.
Browse our range of WRAS-approved potable water tanks
With our range of WRAS-approved potable water tanks, you can be confident in the safe storage of your drinking water. We stock a range of sizes from 5 litres to 25,000 litres making them suitable for a variety of commercial and industrial applications.
For further information on our range of potable water tanks, please contact our sales team on 01777 858009 or email sales@kingfisherdirect.co.uk.
