Hot and cold water is essential to the welfare of everyone in a building, and it is the one service a building cannot operate without. A building can manage for a while with a lift out of action, or with part of its heating off. It cannot manage without water that arrives, at the right temperature, at every outlet that needs it. When the water cannot be relied on, a building can be forced to close.

So when we are asked whether a client can afford continuous monitoring sensors, we would suggest it is the wrong question. The better one is what the current approach is costing, what it could cost if the water fails, and what it actually tells you about an essential service.

This is the fourth and closing article in our series on troubleshooting persistent Legionella issues. The framework we use is MOD: Mechanical failure, Occupant behaviour and Design. We suggest that persistent Legionella issues fall into one of those three categories, and that troubleshooting by category, rather than treating symptoms, is the quickest route from a positive result to the actual cause.

The first three articles covered one letter each. This one steps back to make the case for what connects them.

Where MOD Leaves Us

Mechanical failure is the cause that sits between the monitoring points: a passing TMV, a subordinate return loop that has dropped out of circulation, or a dead leg whose position needs to be considered alongside the sampling results. In our experience, around 60% of the mechanical causes of persistent Legionella issues we investigate trace to hot water return problems, and a single reading at an accessible point rarely shows them.

Occupant behaviour is the system that is sound but not used as designed. Demand is lower than the design expected, flushing has to stand in for it, and the proof that flushing happened is a signature. A signature shows a task was logged as done. It cannot show that the water responded.

Design is the risk that was built in. Oversized pipework, low-flow fittings and changed occupancy can leave water sitting in the system, and that cannot always be flushed away or swapped out. It has to be assessed and then managed over the life of the building.

The common thread is that in every case something happens between visits that a monthly reading cannot see. An intermittent mechanical fault, a flush that was logged but did not do its job, a design risk that does not change from one visit to the next. That is where the case for sensors begins.

What Manual Legionella Temperature Monitoring Can and Can't Tell You

Manual temperature monitoring takes a reading at a given outlet on a given day. It is a snapshot. A reading within range tells you the system was within range at that point on that day, and nothing about the days either side of it.

That is what the method was built to do, and it does it. It produces a compliance record. What it does not produce is a picture of how the system behaves between visits, which is where, in our experience, many persistent problems actually develop.

It is a point-in-time method, and the limitation sits in the method, not in the people carrying it out. A programme that relies on one reading a month may produce a consistent record without revealing problems developing elsewhere in the system.

Three Reasons Legionella Monitoring Sensors Make Sense

Cost. ACoP L8 asks duty holders to reduce risk as far as is reasonably practicable, which means weighing the cost and difficulty of a control against the risk it addresses.

That test moves as technology and prices move. A control that was out of proportion some years ago may not be now. At a site with a persistent problem, the comparison is not sensors against nothing. It is sensors against the cost of disinfecting the water system, repeat sampling, remedial work and the visits that go with all of it.

It is also sensors against the cost of a building having to close, which can mean lost time, lost money and reputational damage. Weighed that way, we would suggest continuous monitoring can be a proportionate response, particularly where routine checks are not providing enough information to identify the cause.

Occupant welfare and the risk of closure. The duty under ACoP L8 exists because the people in the building are exposed to the water in it, and some of them are more vulnerable than others.

Hot and cold water is also essential to their welfare day to day, for drinking, washing, using the toilet and keeping the place clean.

The longer a fault runs undetected, the longer occupants may be exposed to the associated risk, and the greater the chance of disruption to the water supply. Where a building cannot safely provide water, it can have to close, in whole or in part, and that can cost time, money and reputation.

Continuous data can shorten the time between something going wrong and someone knowing about it, which gives a chance to act before a problem reaches that point.

Exposure if a positive result reaches the media. A positive result is a compliance matter first. It can also become a public one.

An organisation that can show what the water was doing, and what was done about it, is in a very different position from one that can only produce a monthly log.

Insight and Accountability

Sensors can strengthen compliance records by providing a more detailed picture of system temperatures and trends, alongside the inspections, maintenance and other checks that remain necessary.

But that is only part of the case. The greater value is in the insight and accountability they provide.

Insight is being able to see what is happening and identify developing problems earlier. A hot water return that has dropped out of circulation can show in the data when it happens, rather than waiting for the next routine visit. A cold supply creeping towards 20°C over several weeks can show as a trend before it crosses the threshold.

Where the monitoring system is configured to assess outlet usage, the data can also help identify outlets that are being used infrequently.

The reading stops being simply a record of the past and becomes a more useful picture of a service the building cannot do without.

Accountability is the record that results. Where flushing is carried out, appropriately positioned sensors can provide evidence of how the water responded. Where something is corrected, the data can show when temperatures returned to the expected range.

The question we raised in the second article was not "is there a flushing regime?" but "how do we know it is working?"

Continuous monitoring gives us more information to answer that question, without relying solely on someone's recollection or a single recorded reading.

This is what Legionella Watch is designed to provide: continuous visibility of water system performance, helping building managers investigate recurring problems, identify changes earlier and understand whether corrective action has had the intended effect.

What It Looks Like by Sector

The operational benefits differ depending on the building and how its water systems are used.

Schools. Better oversight during holidays and closures, when buildings may be used less frequently and stagnation risks can increase. Remote monitoring can also reduce the need for some routine temperature monitoring visits.

Hotels. Earlier warning of hot water problems gives maintenance teams a better opportunity to investigate before guests are affected.

Housing. Problems with hot water can be identified sooner, with a record of system performance available when landlords need to understand what happened and when.

Healthcare and care settings. Protecting vulnerable occupants. Where the people in the building are least able to cope with a failure, knowing about it sooner matters most.

Commercial and facilities management. One continuous picture across a portfolio, rather than relying solely on separate periodic logs from individual sites.

In each case, the operational benefit sits alongside better information for managing Legionella risk.

The Trade

It is tempting to see sensors as an addition to what is already spent. We would suggest that, in the right circumstances, they can change how some of that existing monitoring budget is used.

Today the cost sits in site visits, labour, travel, sampling and reactive work. Some of the visiting effort is spent taking temperature readings, and some reactive work becomes more expensive because a fault was found late.

Continuous monitoring can reduce the need for certain manual readings, and by identifying faults earlier it may also reduce the reactive work that follows.

Inspection, cleaning, servicing and disinfection where needed still happen. What changes is that decisions can be informed by what the water is doing between scheduled visits, rather than relying entirely on the calendar.

There is also a cost that does not appear on an invoice until it arrives. If a building has to close because it cannot safely provide water, the cost can be measured in time, money and reputational damage, and a point-in-time method may give little warning of it.

Earlier warning gives a better chance of acting before it comes to that.

The choice is not between paying for sensors and paying nothing. It is whether the money already being spent on routine monitoring and reactive work is providing the information needed to manage an essential building service, and whether some of that spend could be put to better use.

What to Take From This

Hot and cold water is essential to occupant welfare and is the service no building can operate without. A failure can close a building, costing time, money and reputational damage, so the question is not simply whether you can afford to monitor it continuously, but what the current approach can cost you.

Sensors can strengthen compliance records, but the larger gain is operational: identifying problems between visits and leaving a record that helps show how the water system responded.

Weighed against the cost of disinfection, repeat sampling and remedial work, and against the risk to occupants, continuous monitoring can form part of a proportionate approach to managing risk.

Mechanical, Occupant behaviour and Design explain where persistent Legionella issues come from. Continuous data helps identify and investigate those problems earlier, and it is what Legionella Watch exists to provide.

Could You Be Getting More From Your Water Monitoring?

If you're relying on periodic checks across a building or estate, LCS can help you explore whether continuous monitoring could give you better visibility of your water systems, reduce unnecessary activity and identify problems earlier.

Discuss continuous monitoring with LCS

Keith Elwell is Managing Director of Legionella Consultancy Services Ltd. LCS provides Legionella risk assessments, written control schemes and IoT remote monitoring across commercial, healthcare and industrial premises in the UK.