Water Efficiency and Legionella Risk: Could Saving Water Compromise Water Safety?

Why water efficiency can affect Legionella risk

Stagnation is a major issue in the control of Legionella. If water is allowed to sit in pipework or infrequently used outlets, it gives Legionella bacteria a chance to multiply. It’s much harder for Legionella to become established in flowing water. That’s why outlets that aren’t used often should regularly be flushed to combat the issue.

Water-saving devices do not inherently increase Legionella risk. However, where reduced consumption significantly lowers water turnover in a system designed for higher demand, it can contribute to stagnation and other conditions associated with increased microbial risk.

Regular movement also makes it more difficult for biofilm to form. This allows Legionella bacteria to establish itself and to use it as a food source. Biofilm is slimy coating formed from biological material, scale and sediment. Flowing water will naturally move debris out of the water system, thereby reducing the risk of biofilm.

Water flow also introduces fresh disinfectant used to reduce bacteria in the system. Treatments added at a certain point need water flow to move around the system. If this doesn’t happen, treatments will decay in parts of the system with little to no flow. And again, it raises the risk of increased Legionella bacteria.

Finally, stagnant water can become warmer. Cold water flowing through the system will remain cooler than sitting water. If water sits for a while, it’s at risk of warming to the ideal temperature range where Legionella bacteria would grow.

How can water-saving measures increase Legionella risk?

Water saving and Legionella … can they coexist? Absolutely, but you must take care to strike a balance. Let’s look at some of the areas to be aware of.

Low flow taps and shower heads

These save water, but they can also increase the Legionella risk. A slower flow and less water flowing through the pipework increase the chance of bacteria multiplying there. Stagnation and variable water temperatures are a greater risk.

Reduced use of toilets, taps and other outlets

Here’s another example where stagnation becomes more likely. There’s less water movement through toilets and outlets that aren’t often used.

You also need to recognise that when such outlets are used, they’re likely to create water droplets. Legionella bacteria are inhaled through contaminated water droplets or vapour in the air. Reduced usage is riskier in terms of water safety, but in this case, it is also more likely to create the circumstances that are rife for inhaling harmful bacteria if they’re present.

Oversized water storage

Water storage should suit the size of the building and its requirements. If it’s too large, it can pose a greater Legionella risk.

Stagnation becomes more likely. The water temperature may also veer into the danger zone of 20-45 degrees Celsius, the ideal range for Legionella bacteria to proliferate. It may seem ideal to have more water than you need at your disposal, but this can cause other problems with water safety.

Hybrid working and reduced building occupancy

Even if a building was constructed with the best and most appropriate water system in place, needs can change. Modern life has more people working from home and opting for hybrid working than ever before.

When the number of workers in the building drop over time, the water system may present new challenges when maintaining water safety. The daily water turnover changes, sometimes radically. For instance, staff kitchens or showers provided for those who cycle to work may see a significant drop in usage. There could be days where they’re not used at all. This raises the risk of stagnant water, leading to the creation of biofilm and a rise in waterborne bacteria.

Lower hot water temperatures

One way to make a business more energy efficient is to reduce hot water temperatures. However, reduce them too much and you’re in Legionella risk territory again.

Legionella can proliferate where water temperatures are favourable, particularly within the approximate range of 20°C to 45°C. Temperature-based control strategies therefore aim to keep cold water cold and hot water sufficiently hot, while recognising that temperatures at individual parts of a system can vary.

Cold water must always be below 20 degrees, while hot water should be stored at 60 degrees or above, and delivered at 50 degrees or above (55 degrees in healthcare settings).

Water efficiency measures in older plumbing systems

The older the building, the more chance there is that it could be affected in this manner. We’ve already mentioned low flow outlets and shower heads. They’re designed to use less water, a good thing given the need to save water and use it more responsibly.

Yet when they’re fitted into a water system that was designed and installed potentially several decades ago, there’s a major mismatch between the two. The system may now deliver far less water than it was originally designed for. This increases stagnation risk, reduces flow, increases the risk of biofilm formation, and more.

In cases where a business looks at introducing water efficiency measures, the effect this will have on the existing water system, and Legionella risk must also be considered.

The energy efficiency dilemma: Can hot water temperatures be safely reduced?

This is a balancing act. Reducing the hot water temperature saves energy. It also reduces scalding risks in relevant settings. Care homes and hospitals are good examples of this.

However, if we lower the water temperature too much, it’s more likely that we’ll come close to the upper limit for the growth of Legionella bacteria. For example, hot water storage should not drop below 60 degrees Celsius. If scalding is noted as a risk factor for those using the system, thermostatic mixing valves or TMVs can be installed. These reduce the temperature of the hot water just before it leaves the water system via a tap or other outlet.

Put simply, water temperatures can sometimes be reduced to encourage energy efficiency and lower bills. However, this should not come at the expense of water safety. If you’re looking at energy efficiency, Legionella and other waterborne bacteria should always be a major factor to consider.

How changing building occupancy affects water safety

So far, we’ve looked at various risk factors that may be present in any business setting, from an office to a factory. Sustainable buildings will be designed to provide the most efficient use of energy and water. But what happens if the building usage changes?

This can happen in all kinds of settings. Many office buildings now have reduced occupancy and usage due to hybrid and home workers. Hotels have quieter periods with few rooms being used. Multi-occupancy buildings may see periods where some units are empty. Schools and Universities empty out for the holidays.

In these scenarios, those responsible for water safety must consider how the risk factors present at normal times will change. Sustainable water management is admirable, but again, it must also manage Legionella risk.

Legionella risk factors are more likely to arise in low-use water systems. A current Legionella risk assessment should cover all risk factors in a sustainable building. It should be reviewed if or when building usage changes.

Attention should particularly be paid to two things:

• Stagnation risk
• The water temperature range, with 20-45 degrees Celsius confirmed as ideal for Legionella bacteria to multiply
• Water system cleanliness

For example, some outlets may previously have been regularly used. When building usage changes, certain outlets may only be occasionally used. A flushing regime should then be introduced to remove stagnant water and other factors mentioned earlier in this guide. This would be necessary in schools and universities during the holidays, summer months or in hotels out of season, for example.

That’s why Legionella risk assessments are living documents. Whenever there is a change in building use or occupancy, it should be reviewed to see what else must be done to maintain water safety.

Designing water efficiency and water safety together

At times, water efficiency may seem like an entirely different concept to water safety. Yet the two must work together. If you view water safety and sustainability as related topics … which they should be, you’ll find it easier to make sure you’re doing the right things in both areas.

For example, a water system should always be the right size for the business or building it serves. It’s much easier to do this when planning a new building. However, water safety should always be a focus when reviewing how efficient a current water system can be. For example, if the building usage has changed over the years, it would be prudent to remove redundant pipework and outlets. This would remove the associated Legionella risk in those areas, too. It’s a good example of water efficiency and water safety being dealt with together.

If you’re considering how efficient the water system in your building is, think about monitoring usage. Smart monitoring is a good way to really understand what’s going on. The data can also alert to you any potential water safety risk factors.

We’ve covered the possibility of flushing infrequently used outlets already here. If you can’t remove an outlet because it is still occasionally used, think about installing smart flushing rather than relying on a manual programme of flushing.

Efficiency also covers the question of how much water you need to store. You should have the correct size of water storage tank for the building. Stored water can pose a Legionella risk, particularly if you’re storing more than you need. You’ll incur less risk of Legionella if you have the correct size water system, and that could change over time.

Reviewing the Legionella risk assessment whenever building usage changes

A Legionella risk assessment isn’t a document you should complete and forget about. It shouldn’t merely consider the installed water system either. It should highlight all current risk factors, removing them where possible and reducing the risks elsewhere.

Thus, if there’s a change to how the building is used, this could also change the risk factors. We mentioned low use and occupancy above. An increase in hybrid working can reduce the demands placed on the current water system. There could be an increased risk of water stagnation and Legionella bacteria multiplying.

Changing usage requires a fresh look at the current risk assessment. You may need to flush outlets more regularly to prevent stagnant water settling inside the pipework. This is just one example. The point is to remember that your risk assessment is live. If there is a material change in building use, it’s time to review your Legionella risk assessment.

Can smart water monitoring improve water efficiency and water safety?

Smart water monitoring gives you data on water usage, flow rates, and other details in real time. It helps you spot and fix leaks before they become serious. You can also install sensors to check water quality and the water temperature. You’ll receive an alert if the temperature falls into the danger zone for Legionella (20-45 degrees Celsius). Thus, you can see how water is being used and make sure the system is operating safely.

Our real-time Legionella monitoring article looks at this in greater detail. You’ll see how smart monitoring alerts you to issues that you can resolve quickly, before they present real risks to water safety.

Sustainable water management based on current and potential risk factors

The Legionella risk assessment must note all current risks in the water system. However, it should also consider potential issues that could arise in future.

We can use the example of changing usage or building occupancy here. Let’s say a Legionella risk assessment for a university building or campus notes all current risk factors. These will consider the risks that exist when the campus is busy with students and faculty members.

Yet there will be other potential risks that will arise when the buildings empty out for the summer. Infrequently used outlets may not be a feature at other times of the year, but they will be at this time.

These quieter times offer opportunities to use less water. Yet they will also highlight risks that aren’t there the rest of the time. Those in charge of water safety must implement a system that flushes at-risk outlets regularly enough to maintain their safety. This would also be the ideal time to clean shower heads and other irregularly used outlets that could pose a Legionella risk.

Considering potential risks is harder than identifying current ones. If you want to focus on sustainable water management, you need to include all potential risks that could appear when taking this approach, too.

Water efficiency should not compromise water safety

Reducing unnecessary water consumption makes environmental and commercial sense. But water efficiency measures should never be introduced without considering how they may affect the operation, turnover, temperature and hygiene of the wider water system.

The objective is not to choose between sustainability and water safety. A well-designed and properly managed water system should support both.

Where occupancy, water demand or system operation changes significantly, organisations should consider whether their existing water system remains appropriate for the way the building is now being used. That may mean reviewing storage capacity, identifying redundant pipework, managing low-use outlets, monitoring temperatures and flow, or revisiting the Legionella risk assessment. The most effective approach is therefore an integrated one: understand how water is being used, identify where efficiency can be improved, and assess the water safety implications before changes are made.