Building Water Systems Requiring Disinfections

January to May of 2019 saw three different premises, managed by Quantum clients, returning with Legionella results of above 1,000 CFU/L (samples taken by Quantum during Legionella Risk Assessments).

As you may be aware 1,000 CFU/L is the Health and Safety Executive’s (HSE) action level at which significant remedial action, most commonly system disinfection, is required.

System disinfections by their very nature are costly, labour intensive and can be disruptive to business continuity. Hence, they are best avoided by ensuring appropriate Legionella management by the M&E contractor and their Legionella service provider.

With ambient temperatures becoming warmer over the coming weeks, this time of year often sees an increase in reported high levels of Legionella and other bacteria in the water systems within buildings. Cooling towers will be especially prone to this seasonal variation, however hot and cold water systems are affected also.

A review of the high Legionella results found the following contributory factors;

1. Continuous chemical dosing systems installed to provide Legionella control, instead of hot and cold temperatures, not achieving suitable chemical concentrations at sentinel outlets or throughout the system.

A further briefing note is being put together on this topic, however, the key point to note at this time is that like temperatures (where hot water systems should meet a minimum 50 degrees Celsius at all outlets, and Cold Water Systems a maximum of 20 degrees Celsius at all outlets), chemical systems should also be maintained within minimum and maximum concentrations, and this should be monitored monthly by the Legionella service provider.

2. Monthly monitoring by the M&E contractor identified that hot water temperatures were not achieving the correct temperatures for thermal Legionella control, however no further action was taken. Note: It is a requirement of the HSE that regular Legionella sampling is undertaken in the event control measures are consistently not being achieved.

3. The Legionella service providers being employed by the M&E contractor not being members of the Legionella Control Association (LCA). The LCA is presently the only recognised means by which a company can demonstrate competence within the field of Legionella management. Any companies’ membership can be checked by following this link:

Should you require any further information, please feel free to contact Tom De Ronde, Quantum’s Principal Legionella Consultant: