Legionella under the magnifying glass

21 July 2022

Drinking water in Germany is of universally high quality. And it’s the job of Melanie Wiegand from TÜV NORD subsidiary DMT to ensure that it’s clean and safe when it comes out of the tap. In this interview, the trained biologist explains the stages involved in testing drinking water and what else individuals can do to ensure that their own domestic water supply is safe.

#explore: Drinking water is said to be the most studied comestible of all – is that true?

Melanie Wiegand: That’s correct. The very high standards start with the supplier, who is required by law to provide harmless drinking water to consumers. However, the responsibility of the water supplier ends at the domestic stopcock. Each operator is responsible for the installation on their own premises. For example, in public buildings such as schools and offices, drinking water usually has to be tested every year. If there are showers and a large-scale system for heating drinking water, the hot water must also be tested for Legionella. These are bacteria that thrive at water temperatures of 25 to 50 degrees, especially in stagnant water – for example, in barely used water pipes or hot water heaters which are set at too low a temperature. During showers, large amounts of Legionella can get into the lungs in aerosol form. The possible consequence of this is Legionnaires’ disease, a severe form of pneumonia.

 

How and where do you and your DMT colleagues get involved as water testers?

We test drinking water installations in large industrial and commercial buildings. Also in museums, schools and day-care centres – in other words, in public buildings. Any water that is explicitly provided there as drinking water must meet the legal requirements. We start by taking water samples and examining them in our laboratory.

 

And what exactly do you look for under your microscopes?

Ours is a biosafety level 2 laboratory. This means that we study bacteria which are potential pathogens. The highest biosafety level is 4. We also work with a partner laboratory to investigate chemical parameters: lead, for example. This has been banned as a raw material for many years, but you still find it occasionally in some old buildings.

What do you do if you discover something in your home’s plumbing system?

Not every bacterial contamination is cause for concern: A milliliter of water may contain up to 100 different colony-forming bacteria. These are generally harmless unless they are specific pathogens as defined by the Drinking Water Regulation. However, if we detect Legionella contamination, our experts conduct risk assessments and provide specific conclusions regarding the cause, along with recommendations for rectifying the issue. A lasting solution to the problem can only be achieved by analyzing the interplay between water chemistry, physical and hydraulic parameters, and the microbiological conditions within the drinking water system. We monitor and verify the remediation measures through expert assessments and laboratory analyses.

What can each of us do to ensure the safety of our own drinking water?

Even small steps help. The aerator—the small screen at the front of the faucet—should be replaced annually. It also helps to unscrew the screen every now and then and soak it in vinegar to remove limescale and bacteria. The shower hose in the bathroom should also be replaced once a year. And in the morning, you shouldn’t use the very first water that comes out for drinking, brushing your teeth, or making coffee. That’s because the water has certainly been sitting in the pipes for more than four hours. At that point, it’s considered stagnant water. Bacteria and germs thrive in it and multiply.

 

Do you have any tips for vacation?

At my vacation rental, I turn on the sink faucet and let the cold water run first, followed by the hot water, for a few minutes. Then I check the water temperature: if it’s nice and cold and nice and hot, the plumbing is working properly. By the way, this also applies at home: Water should come out of the water heater at a temperature of at least 60 degrees; otherwise, the potential health risk from Legionella bacteria is significantly increased. A quick tip for vacation planning: On the website of the European Centre for Disease Prevention and Control (ECDC), you can find out which hotels in popular vacation destinations have already had Legionella outbreaks linked to cases of Legionnaires’ disease.

What makes your job as a water tester so exciting?

The fact that I can actually get my hands dirty rather than just working with data on a theoretical level. I can literally see what Legionella look like and how many there are. And I can find out the reasons for the load. As a result, we here at DMT have hands-on knowledge of what makes water safe, which gives us the opportunity to protect people through our work.