With the current energy prices, many homeowners wonder why the flow temperature of their hot water system in the building has to be 60°C, although 45°C would be sufficient. A lot of energy and thus money could be saved here. After all, the energy input is not insignificant; in a year, about 600 to 800 KWh are consumed per person for the preparation of hot water, which at current gas prices (Nov 22) is about 600 euros for a four-person household, according to Verivox.

However, precaution is advised here, because pathogens, especially the dangerous legionella, multiply particularly well in the drinking water piping system of buildings at temperatures between 25 and 50 degrees. They find optimal living conditions in the limescale deposits and biofilm of the pipe system. But a high level of legionella in the drinking water endangers the health of the residents. If they inhale aerosols, i.e. the smallest water droplets, when taking a shower, the legionella in the water can enter the lungs and cause severe pneumonia (so-called legionnaires’ disease), which can even be lethal in about 10 percent of cases. In addition to older and chronically ill, immunocompromised people, smokers are also particularly at risk.

However, since legionella hardly reproduce at water temperatures above 55°C and are largely killed above 65°C, a supply temperature of at least 60°C is prescribed for apartment buildings and public buildings. Although homeowners are not obliged to follow the rule, they should do so in the interest of their health.

The German Technical and Scientific Association for Gas and Water (DVGW) recently organised an online conference on this topic with 170 experts from health authorities and ministries, physicians, hygienists and microbiologists, plumbers and experts, and explicitly pointed out that “temperature is the only corrective (that) reliably inhibits the proliferation of legionella and other relevant microorganisms. Therefore, compliance with the generally accepted rules of technology is indispensable for the protection of human health.”

But are high water temperatures really the only way to successfully reduce legionella? Aren’t there more energy-efficient approaches? For years, the Federal Environment Agency has been calling for concepts for effective energy saving in water heating that nevertheless comply with the requirements of the Drinking Water Ordinance. However, the high hot water temperatures are contrary to the goals of climate protection, which call for effective energy saving in residential buildings. Not to mention the fact that the enormous increase in energy prices no longer justifies such an approach.

Within the framework of research projects, solutions are being researched as to how drinking water hygiene can be ensured even with less heat and thus less energy input. The ULTRA-F research project, which has been running together with the DVGW since 2018, examined a new building equipped by Seccua last year. Here, the scientifically supervised field trial is testing whether the installation of an ultrafiltration system at the domestic water inlet (PoE – Point of Entry) can keep the pipe network of a new building free of pathogens such as legionella and amoebae. In contrast to the existing building, where the “contamination” has already taken place, the cause of this problem could be prophylactically and holistically avoided in a new building. In this way, lower temperatures could be considered without hygienic risk… Seccua is working together with TU Dresden and other research institutions on this study, results are expected by the end of 2023. Seccua is working together with the TU Dresden and other research institutions on this study, results are expected at the end of 2023.

The study “Future Strategy for Drinking Water” by the Handelsblatt Research Institute also concludes that ultrafiltration could make a key contribution to saving energy by unnecessarily heating drinking water. “Using membrane filters (with digital self and remote monitoring), bacteria are filtered out of the circulating hot water system. Unlike disinfection, for example, nothing is added to the drinking water, so no new source of danger is created.” Through the interaction with other factors such as an installation system that is as simple as possible and automatic flushes, “the hot water temperature required to maintain hygiene can be reduced by more than ten degrees Celsius. This significantly improves the energy balance of the building.” (Drinking Water Strategy for the Future, page 15).

Seccua agrees with the statement of the Federal Minister for Building, Klara Geywitz, who said: “Buildings are very complex, and therefore we definitely need an openness to technology in the implementation of the Building Energy Act.