PUMPS, WASTE MANAGEMENT & WATER TREATMENT
Preventing legionella in water storage cisterns: crucial to public health
To prevent the growth and spread of Legionella in water tanks, it is imperative to implement comprehensive and proactive prevention measures. In this article, Keraflo discussed key strategies on adopting best practice for preventing legionella contamination in water tanks in order to safeguard public health
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egionella bacteria thrives in warm water environments, making water tanks an ideal breeding ground if not managed properly. In an ideal world we would not use cold water storage cisterns (tanks) for domestic water. However, it is widely accepted that this is not always possible, as there is generally insufficient mains pressure, or flow rate to meet the demands of larger buildings, so we must therefore rely on the use of cold-water storage tanks in residential blocks, commercial buildings and schools to name but a few. There are however a number
of prevention strategies, which can be adopted to ensure that the risk of a legionella outbreak is minimised or preferably avoided. Ideally a cold-water storage tank is designed so that the water is
turned over and replaced every 24 hours, ensuring the water temperature remains as close as possible to the temperature of the incoming supply which is generally around 10 degrees in winter months and up to 20 degrees in the summer months. Maintaining the right water temperature is crucial in preventing Legionella growth, as Legionella starts to proliferate when water temperature rises above 20 degrees so it’s essential that this is continually monitored. There are various approaches when sizing tanks, which tend to be typically oversized and over engineered, to provide for a greater volume of water than the building requires. The fear of not meeting demand outweighs the size of the tank, which can make it very difficult to manage the water in the tank efficiently. Keraflo’s Tanktronic advanced electronic tank management system is capable of constantly and accurately monitoring the temperature inside the cistern (tank) it also provides a two-stage alarm which are relayed back to the BMS so remedial action can be quickly taken when needed. While the use of an advance tank management system is key – it is also important to recognise that regular testing and inspections are fundamental to preventing legionella. If a build-up of sediment, biofilm formation, or temperature increases are detected, the tank will require draining, so that it can be thoroughly cleaned and chlorinated. Many building owners choose to adopt an annual drain and clean, regardless of the inspection outcome, as standard
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practice, under their own risk assessment process. Stagnant water provides an ideal environment for legionella and other waterborne diseases to survive and proliferate. Implementing strategies to prevent stagnation, such as regular water flow through the tank, is especially critical in areas with low water usage. The use of delayed action float valves is an effective way to ensure this is achieved.
It is common that water demands of a building continually fluctuate, for instance, when schools are not being used during weekends or are closed during school holidays. Sports stadiums often have high water demands when an event is taking place and conversely very low demand when not in use. Likewise, office buildings are generally using less water than they used too, due to new hybrid working patterns being accepted. Valves, such as those from Keraflo, provide buildings the flexibility to reduce or increase the volume of the water in the tank, to ensure that there is always sufficient to meet their specific requirements. This solution can also be fully automated, by integrating Tanktronic which has holiday modes built in, allowing for different capacities to mirror demand. Where a tank does not have huge diversity, or a varying demand, the holiday setting can be used to either reduce the capacity or increase the delayed action once a week, so that the tank partially empties before refilling, guaranteeing regular throughput and a healthy water supply. Typically, tanks are designed with a division inside it, to ensure an uninterrupted supply of water to the
building is maintained. While one side (or half) is isolated and drained down for maintenance or cleaning – the other side can remain fully operational to service the building. However, if both sides of the tank are operating, it is essential that both valves fill simultaneously, to avoid a potential risk of a biofilm forming on one side of the tank. This is a surprisingly regular occurrence, especially if the tanks are oversized. If one valve opens up and is able to keep pace with demand, water will backfill through the balance pipe and begin to fill the other side of the tank. If there are two independent mechanical valves, irrespective of type there are no guarantee’s they will operate simultaneously. This, however, can easily be overcome by using a Twin KP valve or Tanktronic system, as this ensures that both sides of the tank are filled at the same time, regardless of if there is a slight imbalance. Preventing legionella contamination in water cisterns (tanks) is crucial for public health and safety. By implementing comprehensive prevention strategies, including regular maintenance, temperature control, disinfection, filtration and monitoring, we can significantly reduce the risk of Legionnaires’ disease outbreaks. Combining these strategies with education and risk assessment can all help ensure that our water systems remain safe and free from these potentially deadly bacteria. Public health authorities, building managers and maintenance personnel must all work together to mitigate the risk and protect communities from legionella- related illnesses.
BUILDING SERVICES & ENVIRONMENTAL ENGINEER DECEMBER 2023 23
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