Recent guidance from Public Health England (PHE) urges business to engage in ‘regular flushing' of water systems at the likes of dental practices, hairdressers, gyms, hotels and office buildings.

Toby Hunt of Guardian Water Treatment said: 'Our evidence shows that flushing buildings during periods of inactivity alone may not resolve potential water quality issues. While it could serve to reduce Legionella bacteria, overall microbiological control is likely to be compromised.'

'We have compared four weeks of sample results from this period last year and now, in London buildings that have been locked down and flushed regularly. Legionella failure results are virtually the same, but the TVC (Total Viable Count - which gives an estimate of the total concentration of microorganisms) failure rates have almost doubled.

'Nearly half of the buildings sampled in the last four weeks have failed TVC results, compared with 24% in the same period last year. As the weather gets warmer, these failure rates are likely to increase.

'Flushing is still important however other measures may be required to ensure control of bacteria in these water systems. We recommend that supplementary microbiological samples should be taken to prove regimes are effective, other actions implemented if required.'

The right approach

While flushing of outlets is essential – it's key to preventing stagnation – this process should form part of a holistic approach to legionella prevention and water treatment in general, with works tailored to the fact that a building has been unused.

Daily and weekly testing and associated tasks must be maintained and in some cases increased. 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.

Legionella is not the only issue. Drinking water may no longer be potable during a long period of stagnation, which could also lead to delays in buildings reopening.

A news report earlier this week said, 'premises are also required to undertake a detailed review of all aspects of their water management system before reopening amid the continuing coronavirus lockdown,' and that '…all aspects of the water management system need to be reviewed before reopening the business, and necessary action will be dependent on the complexities of the system.'

'This last point is important – every system and its' usage is different and should be treated accordingly. If we do not recommission buildings safely, public health will be compromised,' concluded Toby.

Responsible parties should refer to the Legionella Control Associations (LCAs) guidance at www.legionellacontrol.org.uk.