Special published about Legionella and low-temperature hot water systems

The Legionella Special features Frank Oesterholt, Andreas Moerman and Paul van der Wielen (KWR), among others. The third article includes a conversation with Eric van der Blom (Techniek Nederland), Moerman and Oesterholt about Legionella management in the context of low-temperature tap water. The fourth is an interview with Alvin Bartels (RIVM) and Oesterholt about how management technologies work and are applied. On Tuesday, 17 March 2026, Frank Oesterholt will be giving a presentation at the Aqua Nederland fair in Gorinchem
under the title “Legionella still requires serious attention”.

een presentatie over het onderwerp met als titel “Legionella blijft om serieuze aandacht vragen”.

                                                                             Click on the illustration to read the Special.

Drinking water safety

The energy transition comes with new challenges for hot water systems. Lower hot water temperatures may save energy but they can also be more demanding in terms of safety requirements for drinking water. KWR researchers are therefore working on solutions that combine sustainable hot water systems with microbiologically safe tap water.

Energy transition requires new knowledge

Hot tap water accounts for about 80% of energy consumption in the water chain. In the energy transition, sustainable heat pumps and low-temperature heating networks are acquiring a more prominent position. However, because these systems always aim for the lowest possible temperatures from an efficiency point of view, they also involve potential risks: Legionella bacteria thrive precisely at moderate temperatures.

KWR is now looking at whether, and how, sustainable heat networks, heat interface units, boiler tanks and flow-through systems can be used safely at lower hot water temperatures as well. This work is being done with practical arrays and pilot projects, laboratory research, digital models and risk analyses, and collaboration with partners such as suppliers of physical management technologies and fellow research institutes.

Less pathogenic Legionella species

Research also shows that not all Legionella species are equally dangerous. Whereas Legionella pneumophila is responsible for the majority of cases of illness, drinking water mainly contains less pathogenic species such as Legionella anisa. These insights help to make regulations more targeted and effective. At the same time, one conclusion remains: ultimately, temperatures of 60°C at the water heater and 55°C at the tap point continue to be the most robust way of preventing legionella infestation.

Range of management technologies

In the fourth article in the series, Alvin Bartels (RIVM) and Frank Oesterholt discuss the operation, applicability and limitations of management technologies such as thermal management, UF and UV systems, copper/silver ionisation and chemical methods. They point out that the last of these methods should be used only in the last resort when all other options fail and, even then, only in ‘priority systems’ designated by law. By contrast, physical technologies such as UV and UF are much more widely applicable because they do not affect drinking water quality. These technologies could play an important role as smart solutions for safely lowering hot water temperatures.

Collection available now

The full series of articles has now been collected in a digital edition of the E&W Installatietechniek trade journal in collaboration with KWR. The articles (all in Dutch) are:

1. Legionella still requires serious attention
2. Legionella prevention requires the maintenance of the input temperature
3. Focus on most dangerous Legionella bacteria and smarter management
4. Legionella management: thermal, physical or chemical?