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Time to unlock the doors

As more businesses start to reopen, Toby Hunt, from Guardian Water Treatment, warns about unused water systems as a potential breeding ground for legionella bactera 

Lockdown has been an unprecedented time in modern history, with much of the UK’s commercial building stock, shut up and out of action. At the time of writing, lockdown measures have been significantly eased – pubs and hairdressers are open and many more factories and office spaces are making the tentative steps back to normality. But what of the water systems that have been unused during this period? When it comes to these potential breeding grounds for legionella bacteria, it is not just a case of switching things back on. 

Apart from the hopefully diminishing threat of COVID-19, there is another pathogen lurking in dormant buildings that needs attention before occupants return. Legionella bacteria has been having a holiday during lockdown, enjoying the lack of water usage and potential for stagnation. Topped with significantly warmer weather than usual, the perfect conditions for the life threatening bacteria have been created. Letting people back in without due preparation could be dangerous. 

You might be forgiven for thinking that simply flushing out water systems before usage is enough to sort out a bacterial problem. It is not a standalone solution, however, and we urge responsible parties to proceed with caution when it comes to this task. While it might get rid of legionella, that’s not the only bacteria floating around in our water systems. 

In fact, we have evidence that flushing buildings alone during periods of inactivity could serve to compromise general microbiological control. Guardian has been sampling buildings throughout lockdown, and in the last four weeks of May, TVC (Total Viable Count) significantly increased in nearly half of the properties we manage – a rise of on average 24% in the same period last year. Now, as we enter yet another heat wave, it’s likely that these rates will increase further. 

Don’t rely on flushing… 

Flushing is important, but should not be viewed as a standalone activity. Other steps may be required to ensure control of bacteria in these water systems and supplementary microbiological samples should be taken to prove regimes are effective. Drinking water in particular needs to be tested – after a long period of stagnation it may no longer be potable, which could also delay buildings re-opening. 

So what is the right approach to managing water systems during lockdown? 

While it might seem that a dormant building needs less attention, in some cases the reverse is actually true. Water systems are designed to be used. 

Where possible, locations in which stagnant water can thrive should be reduced by cutting tank capacity or the number of tanks in use. In buildings with cooling towers, daily and weekly testing, plus associated tasks should be upheld, unless it’s impossible to access the site to carry out maintenance – this was true in some cases when lockdown was at its peak. 

If access is really not an option, the cooling tower and associated systems can be shut down. According the Legionella Control Association, simply reopening a building that has stood idle without addressing the safety of its water systems is unacceptable and likely to be in breach of the law. 

When legionella’s not the problem 

Not all water systems need to worry about legionella. Closed systems pose little risk to human health, but as an integral part of most HVAC systems, keeping them in good condition is key to preventing expensive repairs and breakdown. Corrosion is the scourge of closed water systems, but thanks to the latest remote monitoring technology, ensuring conditions are at the optimum is easier than ever before, while assisting with minimal site visits and social distancing protocols. 

As we enter the ‘new normal’, this approach could become increasingly commonplace; a solution which both improves the efficiency and reliability of closed circuit systems and potentially reduces in-person maintenance requirements. 

Safety first 

We all want coming out of lockdown to work, for the state of our businesses, family lives and well-being. To make it work we have to proceed with caution, be sensible and assess risks. If buildings fail us – either by compromising people’s health or due to expensive repairs and downtime – a smooth transition will be harder to achieve. 


• Increased flushing for little used outlets. 

• Extra microbiological sampling, to check any changes in activity have been effective. 

• Tank flushing – any site with a tank should increase flushing of tank fed outlets. Where possible, tank capacity should be reduced. 

• Water heaters can be turned off if hot water is not required – as long as the water is stored at less than 20°C. Outlets should be flushed daily or as frequently as possible. 

• Cooling towers – daily and weekly testing and associated tasks must be maintained. Dipslides, TVC and Legionella sampling should continue at the usual frequencies. Total shutdown should be avoided where possible. 

• Water softener – salt level in the brine tank should be checked regularly and topped up if required. It is likely that the amount of softened water required will be less than usual. 


2 September 2020


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