Can Hard Water & Limescale Increase Legionella Risks?

This specialist guide has been written by the water safety experts at Legionella Control International and asks if the presence of hard water and limescale increases the risks from Legionella bacteria and Legionnaires’ disease. The guide looks at the formation of scale in water systems, fittings and appliances and how it can encourage the growth of biofilm and bacteria including legionella. It concludes by reviewing what practical measures can be taken to prevent, or at least reduce the risks that limescale brings with it.

Does hard water and limescale build-up increase legionella risks?

Many elements influence the risk of legionella bacteria growing in a water supply.

The temperature of the water is just one… however, many people do not realise that the chemical make-up of the water supplied is another factor worth considering.

We all know there are hard water areas and soft water areas in different parts of the UK.

All rainwater as it falls from the sky is classed as soft water.

It’s what happens to it once it has reached the earth and on its way to our taps that determines whether we receive soft or hard water.

Rainwater that comes in to contact with lots of minerals in the ground such as magnesium and calcium will end up as hard water.

Rainwater that does not pass through such minerals remains as soft water.

How does water hardness and limescale affect the growth of legionella?

Legionella needs two things if it is to spread throughout a water system of any size:

The optimum temperature range, i.e. between 20-45 degrees Celsius
Available nutrients to feed on

The need for suitable nutrients is where the presence of hard water becomes a potential legionella issue.

In cases where legionella has been present in a hot or cold water system, nutrients are typically found to be present in the form of biofilms.

Testing your water for Legionella bacteria

These biofilms harbour microbes that Legionella bacteria can use as nutrients… and of course, nutrients encourage the bacteria to grow.

Does legionella thrive in hard water areas?

Hard water causes a number of problems the most obvious of which is the build-up of limescale, as you may already know if you live in an area with hard water.

This means kettles, washing machines, dishwashers and shower heads tend to scale up far faster than they would in soft water areas.

To combat the problem you’ll need to descale your kettle and many other appliances in your home too if you want to keep them working as they should.

If you have ever left your kettle for ages before descaling it, you’ll know how furred up it can get inside.

If you look closely, you’ll see there are uneven layers of scale against the inside of the appliance.

The same build-up of scale also applies inside your water pipes.

The fractured and uneven nature of those layers of scale lining your water pipes creates some great opportunities for bacteria and biofilm to start building up in crevices in the scale coatings, and that may not be flushed out by the water supply as it flows through the pipes.

This is great news for biofilm, Legionella bacteria and other pathogens, but not for anyone using that water supply.

It doesn’t mean an outbreak of Legionnaires’ disease would occur, but it does raise the risk of one happening.

Learn more about Legionnaires’ disease

When you consider that hard water can and will affect all manner of appliances, taps, showers, pipework, and other water-related items within a property, you can see that the risk of Legionella bacteria is raised throughout as well.

Research indicates biofilm are not present when internal pipe surfaces are smooth

Biofilm tends to need an uneven surface to form and then colonise a water system.

Learn more about biofilm

So, if you live in a soft water area, the pipes your water flows through are likely to be free from scale and so much smoother inside.

The absence of limescale means you’ll be far less likely to be affected by a build-up of Legionella bacteria in your water system.

However, the opposite is true in hard water areas.

In hard water areas biofilm can far more readily occur encouraged by the presence of scale inside the pipes which creates the perfect scenario for biofilms to develop over time.

What can you do to combat the risk of legionella in hard water areas?

You cannot do much about living in an area supplied with hard water. You could move, yes… but there are other steps you could take to reduce the legionella risks associated with scale.

Regularly cleaning and descaling kettles, shower heads, taps and other appliances and fittings is a positive step and should be done as frequently as is required to keep them scale free.

Water softeners have also proven to be good at reducing scale problems, softening the water supply and therefore keeping pipework and appliances free from scale (or at least in better condition than they were to start with).

It is also possible to install an electronic system or one that uses a magnetic field to remove the harmful minerals from the water supply.

Which properties are most at risk from legionella?

While private homes do have issues with hard water supplies, the biggest concern lies with water supplies used in hospitals, care homes, and other places frequented by lots of people.

In such cases, the presence of hard water should be noted when preparing the legionella risk assessment for the property to identify all potential risks posed by the water system and if risks could be increased by the build-up of scale.

Learn more about the legionella risk assessment process

It is rarely mentioned alongside common risks such as the hot and cold water temperatures, the age of those exposed to the water systems, their health, and other factors such as dead legs in system pipework.

However, as we can see, the chemical make-up of the water present in the system can have a significant bearing on the chance of legionella being able to grow to potentially hazardous proportions.

Scale is a known legionella risk factor, leading to opportunities that will encourage biofilm to grow.

Limescale build-up and legionella in hard water areas

Stopping the scale from forming – or at least significantly reducing its presence – means less chance of biofilm formation and removing a potential food source for the bacteria to feed on.

That alone is a major step in the right direction in the fight to control the growth of Legionella bacteria and preventing potential outbreaks of Legionnaires’ disease.

Legionella and water safety specialists

Our teams of legionella and water safety specialists support those responsible for the control of waterborne pathogens including Legionella bacteria, helping them to protect people and meet their health and safety obligations in this specialist area.

We deliver professional water safety risk assessments for legionella, pseudomonas and other waterborne pathogens, water testing, independent compliance auditing, City & Guilds training and other environmental risk management services that help keep staff and others safe.