A Hello Neighbour guide to keeping your property safe and staying on the right side of the law
It's not something that keeps most landlords up at night, and in the vast majority of cases, it really shouldn't. But Legionnaires' disease is one of those topics that's worth understanding properly, because the consequences of getting it wrong can be serious, and the steps to get it right are surprisingly simple.
At Hello Neighbour, part of what we do is surface the regulation and make it clear, so you can make the right decisions for your property. So let's talk about Legionnaires' disease, what it actually is, how much of a risk it poses to your rental property, and what you can do about it.
So, What Actually Is Legionnaires' Disease?
Legionnaires' disease is a severe form of pneumonia caused by a type of bacteria called Legionella. You catch it by breathing in tiny water droplets that contain the bacteria, not by drinking contaminated water, and not from other people. It is not contagious.
The symptoms look a lot like a bad case of flu at first: high temperature, muscle aches, headaches, tiredness. But it can progress to a persistent cough, shortness of breath, and in serious cases, it can be fatal. Most cases are treatable with antibiotics, especially when caught early.
To give you a sense of scale, according to the UK Health Security Agency, there were 472 confirmed cases of Legionnaires' disease across England and Wales in 2024, with a case fatality rate of around 2.8%. Between 2017 and 2023, annual deaths ranged from 19 to 36 per year. Around half of all UK cases are actually linked to travel abroad rather than domestic water systems. The true number of infections is thought to be higher because many milder cases go undiagnosed, but in the context of millions of rented properties across the UK, the risk in any individual home is genuinely very low.
That said, the people most vulnerable to serious illness, older adults, people with existing lung conditions, those with weakened immune systems, are also often tenants in our properties. So it's worth taking seriously, even if the overall numbers are reassuring.
What Causes Legionella to Grow?
Legionella bacteria exist naturally in the environment. You'll find them in rivers, lakes, and reservoirs, and in very small quantities they're harmless. The problem starts when they get into man-made water systems and find the right conditions to multiply.
The bacteria thrive in water that sits between 20°C and 45°C. That lukewarm range is the danger zone. Above 60°C, Legionella is killed off. Below 20°C, it goes dormant and can't grow.
There are a few things that create the ideal conditions for growth. Stagnant water is the biggest factor, so anywhere water isn't flowing regularly through the system is a risk. Limescale, rust, sludge, and other organic material inside pipes and tanks gives the bacteria something to feed on. And outlets that produce a fine spray, like showerheads, are the main route of exposure because they turn contaminated water into breathable droplets.
In a typical occupied rental property where the heating is on, showers are used daily, and taps run regularly, the risk is naturally low because the water keeps moving and temperatures are managed. The risk increases when a property is left empty, perhaps during a void period between tenancies, over student holidays, or while renovation work is being carried out.
How Does This Affect Letting a Property?
As a landlord, you have a legal duty of care to make sure your property is safe and free from health hazards. That includes the water system. Under the Health and Safety at Work Act 1974, landlords are classified as self-employed and must take reasonable steps to protect their tenants from risks, including exposure to Legionella.
This applies whether you rent out a whole house, a flat, or even a single room in your own home.
In practical terms, this means a few things. Before a new tenancy, you should flush the entire water system and carry out or review a Legionella risk assessment. During a tenancy, you should make sure your tenants know the basics of keeping the water system healthy. And if a property sits empty between lets, you need to be running the water through at least once a week.
The good news is that the HSE recognises most residential rental properties are low risk, provided they have regular water usage and standard domestic-type water systems. They've been clear that compliance doesn't need to be burdensome or costly for most landlords. A basic risk assessment is usually all that's needed, and many landlords are perfectly capable of doing it themselves.
What Does the Law Say?
There isn't a single standalone “Legionella law” for landlords, but your responsibilities are covered under several overlapping pieces of legislation.
The Health and Safety at Work Act 1974 places a general duty on you to protect the health and safety of your tenants. The Control of Substances Hazardous to Health Regulations (COSHH) require you to assess and control risks from hazardous substances, and that includes biological agents like Legionella. The Approved Code of Practice L8 then provides the detailed, practical guidance on how to manage Legionella risk in water systems.
Here's the important bit: you are legally required to carry out a risk assessment. However, for most residential properties, the HSE says this doesn't need to be an in-depth professional assessment. You don't need a formal certificate or testing report in the way you need an EPC, EICR, or Gas Safety Record. The exception is Scotland, where landlords are legally required to have a formal Legionella Risk Assessment in place.
If you don't feel confident assessing the risk yourself, professional assessments typically cost between £60 and £300 depending on the property size, and they usually take less than an hour.
The HSE and local authority inspectors do not proactively inspect domestic premises for Legionella, and they won't come knocking asking for evidence of a risk assessment. However, if a tenant were to contract Legionnaires' disease from your water system, you would need to demonstrate to a court that you had taken reasonable steps. That's the point at which having records really matters.
What Are the Real Penalties?
Let's be upfront about the risks here, because the consequences of failing to manage Legionella properly are significant.
Under the Health and Safety at Work Act, fines for non-compliance can be unlimited. Landlords can also face imprisonment in severe cases, particularly where negligence leads to a death. And here's something that catches a lot of landlords off guard: you can be prosecuted even if nobody actually becomes ill. It's enough that your tenants were exposed to the risk.
To put real numbers on this, in one of the most high-profile UK cases, Sanctuary Housing, one of the country's largest housing providers, was fined £900,000 plus over £11,000 in costs after Legionella was found in all 44 water samples at one of their sheltered housing schemes. Their staff had been inadequately trained, they failed to respond promptly when Legionella was first detected, and residents were allowed to continue using contaminated water without proper warning. Remarkably, nobody became ill, but the fine still stood.
In another case, a housing association was fined £12,000 after a resident was hospitalised. They had actually commissioned a risk assessment, but the findings weren't acted on quickly enough.
Some London boroughs can also impose enforcement notices and penalties of up to £30,000 through licensing conditions.
Now, it's worth keeping perspective. These are predominantly cases involving larger organisations, institutional landlords, and sheltered housing with more complex water systems and vulnerable residents. Prosecutions of individual private landlords for Legionella alone are relatively uncommon. The risk for a well-managed residential property with regular occupancy is genuinely low. But “uncommon” doesn't mean “impossible,” and the financial and legal exposure if something does go wrong is enough to make a simple risk assessment very worthwhile.
How to Keep the Risk Low
The reality is that preventing Legionella in a standard rental property comes down to a handful of sensible, low-cost actions.
Keep hot water hot and cold water cold. Set the hot water cylinder to store water at 60°C or above, and make sure cold water stays below 20°C. This single step makes the biggest difference because it keeps water out of the temperature range where Legionella thrives.
Flush the system before a new tenancy. Run every tap, shower, and outlet for at least two minutes before a new tenant moves in, particularly if the property has been sitting empty.
Remove any dead pipework. Old or redundant sections of pipe where water can sit and stagnate should be taken out. These are one of the most common hidden risk factors.
Keep water tanks covered. Cold water storage tanks should have tight-fitting lids to stop debris, insects, or other contaminants getting in.
Think about your boiler setup. Combi boilers and electric showers reduce the need for stored water, which naturally lowers the risk.
Talk to your tenants. Let them know they should clean and descale showerheads regularly, use all the taps in the property at least once a week, avoid adjusting the hot water temperature settings, and tell you straightaway if they notice anything unusual with the water, such as discolouration, lukewarm cold water, or a boiler that isn't working properly.
Manage void periods. If a property is going to sit empty, run the water system through at least weekly. For longer vacancies, consider draining the system completely.
Keep records. Document your risk assessment findings, any control measures you've put in place, and the dates of system flushing. These records are your evidence of compliance if you ever need them.
What If Legionella Is Found in Your Property?
If you suspect or confirm Legionella in your water system, you need to act quickly and decisively.
The first step is to restrict use of any outlet that produces a fine spray, particularly showers. Tenants should be clearly informed and given practical guidance on what they can and can't use while the issue is being resolved.
Then bring in a water treatment specialist. They can carry out detailed testing, identify where the contamination is, and recommend the right course of action. This usually involves a thermal disinfection, where the entire system is heated above 60°C and all outlets are flushed at high temperature, or a chemical disinfection using agents like chlorine dioxide. All affected components, including showerheads, taps, and tanks, should be thoroughly cleaned and descaled. Any dead pipework should be removed entirely.
Once the treatment is complete, the water should be re-tested to confirm the bacteria have been eliminated. Keep detailed records of everything: the initial findings, the remediation work, the re-test results, and all communication with tenants.
After that, update your risk assessment and put a plan in place to prevent it happening again.
The Bottom Line
For most residential landlords, Legionnaires' disease is a low-probability risk, but one with potentially high consequences if it's ignored. The good news is that keeping on top of it doesn't require specialist knowledge, expensive equipment, or ongoing professional services. A basic risk assessment, sensible temperature management, regular flushing, and clear communication with your tenants will cover the vast majority of situations.
At Hello Neighbour, we believe in making the complex stuff simple. That's what we do. If you're ever unsure about where you stand on Legionella compliance, or any other aspect of managing your rental property, we're here to help. Get in touch and we'll point you in the right direction.
This blog is for general guidance only and should not be taken as legal advice. For the latest official guidance, visit the HSE website at hse.gov.uk/legionnaires or speak to a qualified professional.
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