The rapid spread of the Covid-19 pandemic around the globe, pushed governments to apply strict measures which has affected each and every one of us. Excluding the priority health services, the taken measures have shaken the fundementals of the economies in terms of education, finance, industrial and agricultural production, supply chain management, tourism, transportation and communication. Although, the world has started to return to “normal”, there still needs to be paid attention to the less known devastating hidden colleteral damages. By disrupting essential health services, offices, schools, hotels, and other buildings, the pandemic gives another deadly disease more space to spread and claim lives; Legionnaires' disease.

Legionella is a rare but serious disease caused by inhalation of water droplets containing the pneumophilia bacterium. While there are over 40 types of Legionella, the most dangerous and most critical for the mechanical installations is the type of Legionella pneumophila, which causes Legionnaires' disease. The bacterium Legionella pneumophila and related bacteria are common in natural water sources such as rivers, lakes and reservoirs, and can be found in soils and mud but usually in low numbers. However, the conditions are rarely right for people to catch the disease from these sources. In order for Legionnaires' disease to occur, water contaminated with Legionella bacteria which can spread in droplets small enough for people to breathe in must be inhaled in aerosol form. Thus, the bactaria can goes into the lungs and cause the disease. The infectiousness of the Legionella is directly proportionate to the temperature, PH value of the water, the iron oxide ratio in the environment and the pollution factors that create a suitable environment for the bacteria's incubation period. In order for bacteria to live and reproduce, the most suitable environments for the formation of these conditions are mechanical installation systems.

Bacteria causing Legionnaires' disease despite the techniques used during the processing of water (regardless of how well the mains water is conditioned), even in very small concentrations, can pass into the water from the waters of the nature to the city mains. That is the reason why the bacteria may be found in purpose-built water systems such as hot and cold water systems, cooling towers, steam condensers, evaporative condensers, water filters and unused pipe systems. The lime layers that are constituted at faucets and shower heads are suitable areas for bacteria to settle and multiply.

The most effective method to prevent the infection of the disease to humans is to prevent the spread and reproduction of the bacteria. Since these processes will occur in mechanical systems, the main area of fight is building installations (to keep disease down). The water temperature required for optimal Legionella growth is between 25°C and 45°C, which is the commonly designated temperature in domestic water systems. This possibility increases especially when the usage is discontinous and the water remains stagnant. Areas with no flow or movement in water tanks also create suitable growth areas.

Legionella potential in domestic water installation, according to the researches, decreases to 25% if the hot water tanks (water heaters) are set at 60 °C and above. While there was no Legionella bacteria in the tank, Legionella was found in faucets at a rate that did not pose a risk. If the inner surfaces of the water heater are covered with a dirt-repellent and cleanable material, it carries a lower risk of Legionella compared to tanks with dirty surfaces and dirty-looking water. If the bacteria numbers (total viable count) in the cold water system is low, it creates less risky ambience in the domestic hot water system. However, water temperature is a very important parameter.
In houses, the biggest risky factor is the presence of uncapped water tanks. Research results show that; with well designed system, correct implementation, operation with punctual maintenance, threats in mechanical installations can be avoided.

The risk assessments for the detection and quantification of Legionella bacteria and the disinfection of the water systems should be carried out in this period while life return to normal and the water systems will be reopened and commissioned. There are various disinfecting methods developed against Legionella. Heating and rapid pouring which is the most applicable method is carried out by heating the system to at least 66.1°C and then circulating the water in the system. 90% of Legionella have been isolated from hot-water systems up to 60 °C during 25 minutes; however, at temperatures above 70 ºC they are destroyed almost instantly. If the facilities have been closed for a long time and the water has been still for a long time, it is recommended to increase all hot water tanks to 70°C and maintain this temperature for at least 24 hours. Water should flow from all taps and ends in the hot water installation for 5 or 10 minutes, and the temperature of the water flowing from here must be above 60°C. If this temperature cannot be reached, the operation will fail. This process increases the potential for scalding and should only be done for very well controlled circumstances.

Another effective method is to keep the bacterial risk in building water systems under control by means of disinfectants. Examples of long-term disinfectants added to water to increase the disinfectant level of the building water supply and limit Legionella growth include chlorine, mono-chloramine, chlorine dioxide, ultraviolet light and ozone. The chlorination method is carried out by circulating high-concentration chlorine into the hot water system and squirting until it leaves the system. Chlorine slows growth, but Legionella has a high resistance to chlorine. High chlorine concentration is required for disinfection. However, in potable water systems since high concentration will not be safe, the applied disinfection method should be done in a controlled circumstances. The ozonation method is carried out by injecting ozone produced by the ozone generator into the water system. Ozone dissolves in water at a rate of 1-2 mg per liter and kills Legionella bacteria. The Ultraviolet Heating Method kills Legionella bacteria by sending ultraviolet (UV) rays before they enter the building water distribution system. Disinfection of domestic hot water systems by chemicals, since there is a risk of water consumption, is not considered safe, however, any disinfectant method to be applied should be completed in a controlled manner.

In domestic hot water systems, the most practical way of protection from Legionella bacteria is copper-silver ionization. The effects of Legionella bacteria can be avoided without harming people with this method. The building should be reopened when the safety of the system is taken under control by purifying the hot and cold water systems from bacteria as much as possible.

Regardless of how purified and conditioned, all water systems are at risk of this predictable and preventable contamination. However, discontinous interruptions to the use of buildings and equipment and prolonged stagnation of water carry a high risk of Legionella outbreak. Effective disinfection, maintenance and operation of buildings and equipment will help prevent biofilm, organic residue and corrosion from contaminating the water system; Thus, it will be possible to prevent the formation of a habitat for Legionella.

İmge Karakoç
Business Development Engineer