Reverse Osmosis Water Filter: Can It Help Prevent Legionella in UK Water Systems?

Clean water matters. Whether you’re at school, home, or work, you want your water safe. Reverse osmosis is a method many use to get better drinking water. It removes lots of unwanted stuff. But can it help stop Legionella? That’s a different story. In this post, we look at how RO systems work, what they’re good for, and if they can help with Legionella in UK buildings.

What is a Reverse Osmosis Water Filter?

A reverse osmosis water filter is a system used to clean water. It works by pushing water through filters to remove things like dirt, salt, chemicals, and some bacteria. The water that comes out is called purified water. RO units are often found in kitchens, under the sink. People use them to get cleaner drinking water. They help with taste too. This kind of filter system is useful when the tap water isn’t great. But while it works well at the tap, it doesn’t clean your entire water system. That’s why it can’t fully stop Legionella on its own.

How Does Reverse Osmosis Work?

Water goes through a few steps in an RO system. First, it moves through one or two pre-filters. These catch bigger things like dirt and rust. Then comes the main part—the RO membrane. This is where most of the water filtration happens. Tiny holes in the membrane block things like salts and bacteria. After that, the water might go through another filter to improve taste. Some water becomes waste and gets flushed out. The clean water is stored in a tank, ready to use. All this happens quietly, behind a cupboard or under the sink.

Pre-Filtration: This part comes first. It helps remove particles that are easy to see, like sand or rust. Chlorine gets taken out, too. Chlorine can damage the RO membrane, so it’s important to remove it early. Pre-filters also help the system last longer. If you skip this part, the filters might clog or break sooner. It’s a key step in the whole water purification process.
Reverse Osmosis Membrane: Here’s where the main job happens. The membrane has small holes—too small to see. They let water pass through, but stop most other stuff. That includes heavy metals, bacteria, salts, and even some viruses. Ifthe water pressure isn’t strong enough, it won’t work well. This is the part of the system that really purifies the water. Without it, you’d just have a basic filter.
Post-Filtration: After the membrane, water goes through one last filter. This is often made of carbon. It removes odd smells or tastes in water. Even after all the earlier steps, this one helps tidy up the final product. Some people say RO water tastes flat, and this step helps improve that. It’s not always needed, but it’s often included.
Storage & Distribution: Clean water is stored in a small tank, waiting for you to use it. The water travels through pipes to your drinking water tap. But here’s the catch—if the pipes or the tank get dirty, the clean water can become unsafe again. Legionella likes warm, still water. So if the water sits too long, or if the system isn’t cleaned, bacteria can grow. That’s why good storage matters.

Choosing a Reverse Osmosis System

There are many types of RO units. Some are small and fit under the sink. Others are bigger and can serve more taps. When choosing one, think about your water needs. How much water do you use each day? What’s in your water now? Some systems have extra filters or features. Others have basic setups. Inline filters are useful because they’re easy to change. Make sure your water pressure is high enough—low pressure might need a pump. And always read the instructions carefully.

Key Features of Reverse Osmosis Technology

RO systems are known for their strong cleaning power. They help improve water safety and taste. But they also have some limits. It’s good to understand what they can do—and what they can’t.

Removes up to 99% of Contaminants: RO filters are very good at removing unwanted stuff from water. This includes lead, fluoride, chlorine, and bacteria. Some systems can remove over 99% of harmful substances. That’s why many people trust them for better drinking water. But the exact results depend on how well the system is looked after.
Produces Ultra-Purified Water: RO systems give you ultra-purified water. That means most of the minerals, salts, and other things have been taken out. The result is very clean water. Some people like to add minerals back in for taste or health reasons. Still, this kind of water is safe for drinking, cooking, and pets.
Requires High Pressure: Reverse osmosis works best with strong water pressure. If the pressure is too low, the water can’t pass through the membrane well. Some buildings may need a small pump to help. Without enough pressure, you’ll get less clean water, and it might come out slowly.
Generates Wastewater: Here’s a downside—RO creates wastewater. Not all the water that enters the system comes out clean. Some of it goes down the drain. Newer systems try to reduce this, but there’s always some waste. If saving water is important to you, this might be a concern.

Reverse Osmosis and Legionella Bacteria

Now let’s talk about Legionella. This bacteria can live in water systems, especially if the water is warm and still. An RO unit can purify water at one point, like a kitchen tap. But it won’t clean your whole building’s pipes and tanks. That’s where Legionella often hides. So while RO gives you clean water to drink, it’s not enough to stop Legionella by itself.

It Only Treats Water at Specific Points: RO systems only work where they’re installed. If the system is under one sink, it won’t protect your showers, tanks, or other taps. That means Legionella could still grow in other parts of the system. RO can’t help with that.
It Does Not Eliminate Biofilm: Biofilm is a slimy layer that sticks to the inside of pipes and tanks. Legionella likes to hide in it. RO systems don’t clean biofilm because they don’t reach it. Even if the water is clean at the tap, it might have passed through biofilm before that. So there’s still a risk.
It Requires Frequent Maintenance: If you don’t clean your RO unit, it can stop working properly. Filters get blocked. Tanks can get dirty. Bacteria can start to grow. You need to follow the instructions and replace parts on time. If not, you could end up with more problems than you started with.
It Produces Wastewater: This wastewater has to go somewhere. If it stays in the system or pipes for too long, it can become stagnant. And stagnant water is exactly where Legionella likes to grow. That’s one more reason RO isn’t enough on its own.

Reverse Osmosis and Viruses

RO filters can remove many viruses. The membrane blocks most of them, just like it does with bacteria and chemicals. That makes RO a good choice when you want safer drinking water. Still, viruses can survive in storage tanks or pipes if the system isn’t cleaned. So even though it helps, maintenance is key.

What Other Contaminants Can RO Systems Remove?

RO units can clean out more than just bacteria and viruses. They’re useful for getting rid of things that affect taste, health, and safety.

Heavy metals: RO systems remove metals like lead, mercury, and arsenic. These can come from old pipes or polluted water sources. Drinking water with heavy metals can cause health problems, so removing them is a big advantage.
Chemical pollutants: Things like pesticides and cleaning products can get into water. RO filters help remove these chemicals. This makes the water safer to drink, especially in areas near farms or factories.
Dissolved solids (TDS): TDS stands for total dissolved solids. These include salts, minerals, and metals. High TDS levels can make water taste strange or cause build-up in kettles and pipes. RO systems reduce TDS to give you cleaner, better water.

Reverse Osmosis is NOT a Standalone Legionella Control Method

RO units help with clean drinking water. But that’s just one part of the puzzle. They don’t stop Legionella from growing in pipes, tanks, or showers. So while RO has its benefits, it’s not enough by itself. You need other steps to stay safe.

Does Not Prevent Legionella Growth in the System

RO only treats the water that goes through it. It doesn’t stop Legionella from growing elsewhere. If the rest of your system is warm and unused, bacteria can spread. You need wider water system care to control it properly.

Impractical for Large Water Systems

Using RO for a small kitchen tap is fine. But for a whole school or office? That’s not practical. You’d need a system at every tap, and the cost would be very high. RO isn’t built for full-building use.

High Maintenance

RO filters need regular changes. Pipes and tanks need to stay clean. If you forget or delay, it won’t work well—and could become unsafe. Maintenance is not optional. It’s a key part of keeping water safe.

UK Regulations Do Not Recognise RO as a Primary Legionella Control Measure

In the UK, guidelines like HSG274 and ACOP L8 are clear. RO isn’t one of the main tools for controlling Legionella. The law asks for temperature control, flushing, and disinfection. RO can be helpful, but it’s not enough on its own.

Importance and Benefits of RO Filtration

Even though RO doesn’t stop Legionella, it still has lots of value. It improves the water you drink, helps protect health, and cuts down on bottled water use.

Efficient removal of pollutants: RO systems remove many harmful things from water. These include chlorine, metals, bacteria, and more. It gives you water that’s clearer, cleaner, and safer to drink.

Improved taste: Because it removes chlorine and other odd flavours in water, RO water often tastes better. It’s smoother and more neutral. This makes it better for tea, coffee, and food too.
Strong adaptability: You can install RO systems in many places. Homes, offices, caravans—they fit well in all of them. Inline filters make them easier to use in tight spaces.
Reduce scale: Hard water can leave limescale in kettles and taps. RO removes the minerals that cause this. That means less cleaning and longer-lasting appliances.
Environmental protection: If you drink RO water, you might buy fewer plastic bottles. That helps reduce plastic waste. Also, modern RO systems waste less water than older ones.
Health protection: RO systems help reduce risks from harmful substances. If your tap water isn’t safe, an RO system adds an extra layer of protection. That can matter a lot for young children or people with weak immune systems.

What is the Best Approach for Legionella Control in the UK?

RO has its place—but not for Legionella. For that, you need a proper control plan. These steps are what health guidance recommends.

Temperature Control: Hot water should be above 60°C. Cold water should stay below 20°C. Legionella can grow in warm water, so keeping water at the right temperature is the first defence.
Biocidal Treatment: Some systems add chemicals like chlorine dioxide. These kill bacteria in the pipes and tanks. This works across the whole system—not just at the tap.
Regular Flushing and Maintenance: If water sits too long, bacteria can grow. Taps and showers should be used regularly. Pipes and tanks should be cleaned too. It keeps things flowing and safe.
Legionella Risk Assessments: Every building should have a Legionella risk assessment. It shows where problems might be and what steps to take. In the UK, this is a legal requirement for many workplaces.
HSG274 and ACOP L8 Compliance: These are the official UK rules for managing Legionella. They explain what steps to follow. Staying compliant helps protect people—and keeps your building legal.

Ensure Your Legionella Compliance with Comfort Services Group

Comfort Services Group is here to help you meet your safety goals. We offer full support for water system care, Legionella checks, and compliance. Our team does risk assessments, flushing, disinfection, and system reviews. If you need to meet HSG274 and ACOP L8 rules, we’ve got you covered. We also help you set up records and plans. Contact us today to keep your water systems safe.

FAQs

When is the RO system useful for Legionella control?

RO systems can help clean water at one outlet, like a lab or dental tap. That’s useful if you need purified water in a small area. But they don’t treat pipes or tanks. So for full control, they’re not enough. You still need flushing, temperature checks, and regular system care.

How often does the RO system need to replace the filter?

Most systems need new filters every 6 to 12 months. Some may need it sooner, depending on your water. If you wait too long, the system stops working well. Bacteria might grow inside. Always follow the manual for filter changes and cleaning advice.

Is reverse osmosis water suitable for long-term drinking?

Yes, it is. RO water is clean and safe to drink every day. It removes many things that don’t belong in drinking water. Some people like to add back minerals for taste. But overall, it’s a safe and reliable option for long-term use.

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Andy Green

Founder & Co-Director at Comfort Services Group

Hello, I am Andy Green Founder & Co-Director at Comfort Services Group Limited, an HVAC commissioning & water treatment company which has been established and operating within the UK for over 20 years.Starting as a Commissioning Engineer back in 1989 I have always sort to work within a cohesive & collaborative team environment with an ethos of building long-term relationships. This over the years has become part of our company core value.
We are proud to share our experience and knowledge and take pride in offering this to all clients when required. If I, or one of the team can help then please schedule a meeting via the office or get in touch via one of our social media platforms.