Maybe you have heard about legionella bacteria, Legionnaires disease, or Legionellosis but you are not entirely sure of the risks involved when it comes to the water systems of your building. An individual infected with this disease may develop a very serious pneumonia which can be lethal in some cases. According to recent studies, only in developed countries there are thousands of ourbreaks every year in which 10 per cent of people actually dies. Also, in 90 per cent of the cases, these outbreaks were perfectly preventable.

In an attempt to aid building managers and owners with handling cooling towers, we are sharing five aspects to consider when it comes to the assistance of mitigating legionella outbreaks in water systems of large buildings.

What exactly is Legionnaire disease?

There are more than twenty five related species of Legionella bacteria in nature. They are naturally present in rivers, streams and lakes and are relatively harmless. The bacteria group responsible for Legionella illness, and the most lethal one, is Legionella pneumophila. It actually becomes a real health concern when it can be found in our water systems.

Why is it a health issue in our water systems and not in nature?

Once the bacteria species becomes airborne, evaporation of water in cooling towers, it has the capability to move through air currents and therefore infect people near the source of contamination. After the infection has happened, a pneumonia can be developed.

Who is at risk?

All building managers and owners with cooling towers or even with evaporative condensers for their spas/whirlpools, misters, ornamental fountains and humidifiers are at risk.

Is there anything we can do to mitigate these risks?

Yes, here are five aspects to consider when it comes to mitigating the risks:

1. Evaluation of the water system: does the building have one or more of the items listed earlier as a risk factor (misters, cooling towers, fountains, etc.)?

• Identify potable water systems
• Location of the systems
• How the water is processed and received
• Identify potential risks with the systems water flow – process flow diagram

2. Water treatment program

• Get a water treatment professional to put in place a water treatment program: Recurring water treatment is needed. Bear in mind that several high performing water disinfection tools are available to avoid recurring and expensive chemical cost.
• Guarantee there is no stagnation of water – Legionella grows in warm waters between 22 to 40 degrees. Guarantee that there are no dead-arms in the water system and make sure there is an adequate water recirculation.
• Make sure that the plan includes a contingency plan in case of outbreak.
• Control and communication: make sure you share the plan with the team and assign clear responsibility of tasks.

3. Limit the spread of mist

• Various solutions available on the market can assist in decreasing the mist spray from travelling from the water systems.

4. Monitor and control

• Monitor locations in key areas
• Establish a schedule to take samples: there are several easy-to-use tools to monitor the bacteria amounts in water. Make sure to include a Legionella testing every month of operation.
• Run a legionella risk assessment regularly.

5. Request help

• There are several water consultants you can get in touch with in order to assist you. They can develop a plan adapted to your building water system.

Utilising temperature control

The main method utilised to monitor and control the risk from Legionnaires disease is indeed water temperature control.

Water services must be operated at temperatures that will prevent Legionella growth:

• Hot water storage cylinders needs to store water at 60°C or more
• Hot water must be distributed at 50°C or more (thermostatic mixer valves have to be fitted as close as realistically possible to outlets, where a scald risk is in fact identified).
• Cold water must be stored and distributed below 20°C.

A competent person should routinely have a look, check, inspect and clean the system, in accordance with regulations of the risk assessment.

You need to identify ‘sentinel’ outlets (closest and furthest to each cylinder or tank) for monthly checking of the distribution temperatures. You need to also check the water storage cylinder temperatures every month at least once and cold water tank temperatures once at least every 6 months.

Stagnant water does favour Legionella growth. To reduce the risk you need to remove dead legs/dead ends in pipes, flush out rarely used outlets (including taps and showerheads) at least once per week and clean and de-scale shower heads as well as hoses at least quarterly. Cold-water storage tanks need to be cleaned regularly and water must be drained from hot water cylinders to check for potential debris or signs of corrosion.

Design systems to reduce or minimise Legionella growth, by:

• keeping pipes as short and direct as realistically possible;
• adequately insulating pipe-work as well as tanks;
• utilising materials that don’t encourage the growth of Legionella bacteria;
• preventing and avoiding contamination, eg by fitting tanks with lids as well as insect screens.

Additional monitoring controls

Water samples must be analysed for Legionella bacteria periodically in order to demonstrate that bacteria counts are acceptable and low enough. The frequency needs to be determined by level of risk, and of course in accordance with the risk assessment.

Other monitoring control systems

Other monitoring methods to control Legionella bacteria growth include silver and copper ionisation as well as biocide treatments (like chlorine dioxide). To guarantee that they remain efficient their application will require suitable assessment as part of the general water treatment program including an adequate installation, maintenance as well as monitoring.