Legionella has been a concern for property owners for years. Although the rod-shaped bacteria are a natural constituent of drinking water, they multiply rapidly under the right conditions, such as stagnant water or temperatures of between 20 and 45°C in the often widely branched piping system. They can enter the human lungs with water droplets or steam, for example when showering. In elderly and immunocompromised people, this can lead to Legionnaires’ disease, a severe pneumonia that is often fatal.

To avoid Legionella levels above the limit or measure value of 100 CFU / 100 ml (colony-forming units per millilitre) stipulated in the German Drinking Water Ordinance, preventive thermal disinfection, i.e. temporarily raising the hot water temperature to over 70 degrees, often in advance of upcoming Legionella tests, is a common practice of many homeowners. However, this cosmetic trick as an alternative to proper and professional operation of the drinking water installation does not solve the legionella problem, is harmful to the pipe system of a building and can endanger the tightness of the pipe installation. This is because the temperature fluctuations lead to different expansion and shrinkage of the materials and thus cause all hot water-carrying components to age prematurely with the result that this can lead to leaks and water damage to the installation.

In addition, it is virtually impossible to ensure the high temperatures of over 70 °C for a sufficiently long period of time in the entire piping system up to the last tapping point. But this would be a precondition for effectively reducing all legionella. To make matters worse, Legionella find protection inside the biofilm that always forms in water pipes, and thus survive the flushes. Studies by the ETH Zurich and Eawag have shown that Legionella can survive temperatures of 70°C even for more than an hour. After 60 minutes at 70°C, a quarter of all legionella were still detectable.

Flushing with hot water is therefore only effective to a very limited extent and would have to be repeated continuously in order to control the problem of contamination over a longer period of time. In areas where the previously heated water cools down, the biofilm and the surviving legionella always create a potential for growth and thus renewed contamination through high legionella concentrations. New germs and a rich supply of nutrients are constantly being flushed into the building from the public drinking water network. The hot water also leads to heavy lime precipitation and subsequently to incrustations, which in turn form an ideal breeding ground for biofilm and microorganisms. Another problem that often occurs is that the thermal disinfection of the hot water line also heats up the cold water line to over 20 degrees. The reason for this is the spatial proximity of the two pipes in a shaft and/or poor insulation. Thus, legionella can suddenly appear in large numbers in the cold water pipe as well, and the problem spreads.

Sustainable nutrient reduction instead of repeated disinfection

Instead of just fighting the symptoms, you have to tackle the problem at its root. A permanent reduction of microorganisms and nutrients from the municipal network is the only way to reduce biofilms in the pipe network and thus also the infestation by pathogens such as Legionella in the long term. Seccua focuses on preventive and maintenance measures to ensure drinking water hygiene.

By installing a Seccua ultrafiltration directly at the house entrance of the water pipe, pathogens, turbid and suspended matter are prevented from entering the house’s piping system. The water is filtered through a high-tech membrane that originates from medical technology. The patented nanotechnology has filter pores that are only 20 millionths of a millimetre in diameter.

In order to effectively sanitise drinking water systems in existing buildings and get the legionella problem under control, Seccua workes with partners to develop a three-step process. In the first step, the drinking water installation is comprehensively cleaned and disinfected in order to significantly reduce the biofilm and the germ load. In the second step, hydraulic balancing ensures that the hot water supply is operated in accordance with the standards. Finally, in the third step, an ultrafiltration system from Seccua is installed at the domestic water inlet, which acts as an effective barrier to significantly reduce the reintroduction of microorganisms such as amoebae and legionella from the public drinking water system.

In new buildings, the rule is: what does not enter the building’s pipe network cannot grow to dangerous concentrations there. For this reason, the Seccua system is installed at the house water inlet before the new building’s pipe network is filled for the first time. This means that only ultra-filtered water is available right from the start, which virtually rules out colonisation by microorganisms such as Legionella. Together with scientific research partners of the Ultra-F project of the TU Dresden, scientific proof of this is to be provided by the end of 2023.