Fighting Legionella in Water Treatment Systems

Dealing with Legionella is one of the primary functions of a complete water treatment system. Since an outbreak of what is now known to be Legionella at an American Legion Conference in Philadelphia in 1976, fighting the spread of this disease has become one of the primary functions of most commercial water systems.

Legionella pneumophila, the strain of bacteria that leads to 90% of infections, is present in nearly all freshwater sources. Lakes, streams, and rivers are the natural habitats for the bacteria, places which are often the sources of municipal water supplies. And while municipalities treat their inbound water supply with a biocide, depending on the municipality, certain levels of Legionella are considered acceptable, however, there is no definitive amount that is known to be safe. Although it is almost certainly present in your inbound water source, the risk is relatively low, as the bacteria needs to be aerosolized in order to become infectious.

Cooling tower systems have become the scapegoats for Legionella breeding. Because of the environment in which cooling towers are located, often on rooftops in direct sunlight, they can easily become hotbeds for breeding bacteria. Cooling tower drift is perhaps the most common mode of dispersion for Legionella and is responsible for the outbreak of the disease in New York City in 2015. Controlling drift, regular testing of water in a cooling tower, and robust biocide plan are all factors in ensuring that cooling towers remain safe from harmful Legionella spread. The emphasis in the last five years has been on regular testing and strict control of drift, especially in New York City where, because of the height of buildings, and the location of cooling towers on the roofs of these buildings, drift is especially dangerous.

Cooling Towers Take the Blame for Legionella

While cooling towers take most of the blame for Legionella outbreaks, since the bacteria is present in nearly all water sources, it is important to have a water management program (WMP) that takes control of the entire system. Sampling and testing the water sources in any given environment is extremely important in a WMP. Even more important is testing in the right locations. For example, in a hospital or healthcare center water obtained from rooms in an ICU, transplant ward, or cancer care center is highly desirable for testing and conversely, water from public washrooms has comparatively minimal value. Legionella appears sporadically throughout a building’s water system, so when taking samples, we place more value in the ones from more desirable locations.

Apart from regular testing, it is important that a WMP has a robust biological contaminant control arm. There are many ways to implement a biocide into a WMP, the most common treatment method is the traditional chemical approach. In recent years, however, there have been advances in non-chemical treatment devices (NCDs). For many, these options offer the promise of sustainability and lower environmental impact than using traditional chemical treatment methods. However, the efficacy of these treatments is still in question. A study conducted by the University of Pittsburgh Department of Civil and Environmental Engineering submitted to ASHRAE in 2010 shows that some of the most promising NCDs are not sufficient to control biological growth in a water system.

NCDs offer a great way to take water treatment into a more ecologically minded era, and the possibilities of these options in water treatment systems is good news for the environment and for the bottom line of customers interested in a less traditional method of water treatment technology. While they may not be a viable option yet, it is worth keeping track of NCDs and their future potential.

ASHRAE Standard 188-2015 is a comprehensive set of guidelines for the testing, mitigation, and treatment of Legionella in water systems. Created over the course of 15 years, the American National Standards Institute introduced the standard in 2015, and it has become the guiding principle for all Legionella control in WMP’s since then. While the American Society of Heating, Refrigerating and Air Conditioning Engineers, more commonly known as ASHRAE, does not police the implementation of the standards, they have set up very clear modes of compliance to various other governing agencies, such as OSHA and The Joint Commission.

The standard also lays out clear operating procedures, testing methods, and a personnel chart to create a clear chain of command. However, ASHRAE 188 is only a set of guidelines, and while it is a helpful reference, the battle against legionella can only be won in practice. Mitigating the risk of an outbreak requires a robust WMP one aspect of which is identifying potential hotspots. Cooling towers and boiler systems are specific places in a system that need regular testing to make sure they are being held at temperatures that will hinder the growth of Legionella.

Careful Planning and Robust Water Management Can Lower Risk

While the risk of Legionella is great, and the consequences are severe, with careful planning and a robust water management program in place to track your water system, it is possible to keep the risks at bay. Adhering to a standard such as ASHRE 188 will help to ensure that the system and the WMP have metrics to measure against to ensure that things are running smoothly. Finding a water services provider who will keep all this in mind is imperative when setting up a plan to mitigate a potential Legionella outbreak.