The new hexamonitor, for drinking water that is biologically even safer

The new hexamonitor is up and running in Waternet’s test hall at the Weesperkarspel production site. This test array for six simultaneous experiments is the result of over a year of multidisciplinary effort during which KWR experts combined knowledge, experience and test facilities from ‘old’ Legionella research with new knowledge and technical options. The new array will make it possible to investigate the possible effects of climate change and the energy transition on, for example, the growth of opportunistic pathogens in drinking water mains – and therefore on the biological safety of our drinking water.

Climate change and the energy transition are leading to higher water temperatures in the drinking water mains, for example due to warmer summers and more underground heating networks. KWR microbiologist Nikki van Bel investigates the resulting impact on the growth of opportunistic pathogens in the mains. These are micro-organisms that can sometimes be present in small, harmless amounts in drinking water but that can flourish at higher temperatures. Van Bel: “We urgently need to know more about the effects of temperature rise on opportunistic pathogens so that we can test measures that will allow us to keep the mains as safe as possible in the future.”

Reuse, selection of new components and intensive consultation

Thirty years of research into the opportunistic pathogen Legionella has not only provided KWR with a lot of knowledge: we also had two test arrays, the old hexa- and pentamonitors, in storage. That turned out to be a fantastic opportunity to reuse, add to and further develop the old test arrays in order to build a new array for studying the effects of climate change and the energy transition. And so, in late 2024, a process began of testing, consultation, devising new solutions, and intensive multidisciplinary consultations. Harry van Wegen and Robbie van Pelt from the workshop built the array in close consultation with colleagues including Van Bel and Anke Brouwer from the laboratory. Van Wegen and Brouwer had also worked with and on the old hexa- and pentamonitors 25 years previously and so they could contribute a lot of practical knowledge. They combined their expertise and experience, and discussed options for reusing old components and adding a careful selection of new ones. “That’s delicate work,” says Brouwer, “because the materials used in pumps and other components can sometimes boost bacterial growth. It’s best, for example, to avoid using rubber. So every time Robbie found a pump that met the technical requirements for the installation, we had to check whether the materials used were also suitable.” Van Bel: “And so he received emails from Robbie asking ‘I’ve found a pump with these materials in it, is that okay?’, and that was of course exactly the approach we needed.”

Compact and safe

It was an enjoyable, but complicated, job for the workshop. Van Pelt: “We purchased a range of new components but we also designed and made a lot of things ourselves, such as the heat exchangers. And I was also happy to see Harry immediately setting a high standard at the outset of the project by arguing in favour of a single compact cabinet that would be big enough to house everything.” Van Wegen: “A closed system is safer to use and more pleasant for the people who have to work with it but it certainly makes the design process a lot more complicated. Even so, I like a challenge.”

Mobile array weighing 600 kilogrammes

The joint efforts resulted in a heavy, and impressive, result in the spring of 2025. The new hexamonitor is a mobile cabinet on wheels weighing 600 kilogrammes that is two metres high, two metres wide and one metre deep. Behind closed doors, water is sent through six (hence ‘hexa’) glass columns in safe and controlled conditions. Heated water circulates in the six columns, allowing us to study how well various species of opportunistic pathogens can reproduce at different temperatures and in the presence of different materials. This makes it possible to conduct comparative experiments in a range of selected conditions. Adding opportunistic pathogens to the columns makes it possible to study their behaviour and for researchers to follow the effects of different temperatures on the growth of these pathogens over a longer period of time.

The new hexamonitor: a mobile cabinet on wheels weighing 600 kilograms, 2 metres high, 2 metres wide and 1 metre deep. Behind closed doors, water flows through six glass columns under safe and controlled conditions.

From Nieuwegein to Weesperkarspel

KWR’s sampler, Erik Bogaard, regularly visits Weesperkarspel to take samples for analysis at KWR.

Proximity encourages new ideas

The day-to-day maintenance on the new hexamonitor requires some time and effort at Waternet but Dignum believes that it’s worth it: “It’s nice to have the new hexamonitor on the premises: that makes it feel more like your own research, your own device. And so then you start thinking about possible applications. We have plans at this production site to add membrane filtration and expand our slow sand filters. This should give micro-organisms even fewer opportunities to grow. So if we repeat today’s experiments in a few years, we should see less growth of opportunistic pathogens. That would be a nice confirmation of the changes we have made.”

Several ideas for new research projects are already circulating in the Waterwijs programme. So the prospects for the new hexamonitor are good: there is still a lot it can explore. KWR is committed to making another robust contribution to the microbiological safety of Dutch drinking water with this new test array.