Tap water: Flush briefly, drink without hesitation
Following isolated discoveries of elevated heavy metals levels in tap water at ETH Zurich in the autumn of 2024, an external report has now signalled the all-clear. However, standing water can still absorb small quantities of lead or nickel from fixtures and fittings. In light of this fact, users should allow taps to run until the water temperature is constant before drinking.?
In the autumn of 2024, ETH Zurich examined drinking water in all university buildings constructed up to 1980. In the vast majority of cases, the drinking water quality proved impeccable. In isolated samples, however, the lead and nickel levels exceeded legal thresholds. As a precautionary measure, ETH Zurich installed water dispensers in the affected buildings and informed the staff based there (cf. Internal news from 03.10.2024). Since the initial inspection, a working group has collaborated with external experts to determine the cause.
Fittings containing lead are widespread
The commissioned external report shows that certain materials used in plumbing fixtures, such as brass, red bronze and chrome plating, can release small quantities of lead and nickel into drinking water if water remains standing in pipes for long periods. This is far from an isolated case: the experts claim that this phenomenon is not specific to ETH Zurich and instead extends to every other building in Switzerland and Europe.
“Lead-containing fixtures – such as taps, fittings and pipe connectors – are widespread. Although the lead concentration in taps has declined consistently in the last 20 years, even newer taps are not completely lead-free,” explains Cosimo Sandre, a water specialist at the Swiss Gas and Water Association (SVGW). “After standing still for a prolonged period, tap water may exceed legal thresholds in isolated cases.” As Sandre explains, the longer the water remains still in the pipes, the more heavy metal could dissolve.
So, why were elevated levels detected in four buildings on the H?nggerberg campus and not in others? Sandre points to this water being left standing in fixtures for longer periods prior to sampling.
“I’m relieved that experts have classified the drinking water situation at ETH Zurich as neither out of the ordinary nor as posing a risk to health.”Ulrich Weidmann, Vice President for Infrastructure and Sustainability
No appreciable risk to health
The good news is that reducing potentially elevated levels of heavy metals is easy: simply allow the tap to run until the temperature is constant before drinking. In most cases, just a few seconds is enough. If water has been left standing for longer periods – after a weekend or public holidays – the recommendation is to run taps for up to two minutes.
After briefly flushing taps, follow-up measurements indicated impeccable drinking water quality. “This makes clear that there was not – and is not – any appreciable risk to health, as the water was only able to absorb very low levels of heavy metals,” explains Leonhard Sigel, an occupational physician at ETH Zurich. Nevertheless, it remains important to minimise our lead and nickel intake over the long term – therefore the recommendation to flush taps before use.
Flushing is worthwhile in all buildings
These recommendations are not limited to older buildings. Newer fixtures and fittings also contain small quantities of lead, which can result in elevated levels if water has been standing for long periods. As a result, flushing taps before drinking from them is recommended standard practice.
Flush briefly, drink without hesitation: Recommendations in brief
- Always flush taps before drinking the water
- Let the tap run until the water temperature is constant (usually just a few seconds, but up to two minutes after a prolonged period without use)
- Rely on frequently used sources (e.g. canteens, bathroom sinks)
- Only consume cold-running tap water
- If the water is cloudy or discoloured, flush the tap until the water runs clear
- It is prohibited to use laboratory taps as a source of drinking water
As Ulrich Weidmann, ETH Vice President for Infrastructure and Sustainability, outlines: “I’m relieved that experts have classified the drinking water situation at ETH Zurich as neither out of the ordinary nor as posing a risk to health. Nevertheless, we will systematically examine the lead and nickel levels in drinking water at all ETH buildings on an annual basis moving forward – in line with tests for Legionella and bacteria. In addition, we will implement measures in future construction and renovation projects to further minimise the potential for heavy metals to leach into drinking water.”
Posters displayed in buildings will inform staff, student and guests of the recommendation to let taps run briefly before drinking from them. In the coming days, the Facility Services team will remove the water dispensers from buildings in which elevated lead and nickel levels were detected last autumn.
You can find further information and answers to frequently asked questions on .
Three questions for Andreas Hofmann, Head of Facility Services and Head of the Drinking Water Quality working group
Andreas Hofmann, taps installed throughout Switzerland contain lead and nickel. Should we be flushing our taps at home?
Yes, if the water has been standing still for an extended period. Flush the tap briefly until the water reaches a constant temperature – especially in rooms you rarely use or if you’ve been away for a while. In kitchens and toilets, where water fixtures are used regularly, the water usually reaches a constant temperature after just a few seconds. However, if we’re talking about the tap in a rarely used hobby room, or in a holiday home that has been unoccupied for two weeks, you should run the tap for two minutes as a precaution. This also helps to fight the bacteria that can develop in standing water.
Isn’t it wasteful if everyone flushes their taps before drinking?
There’s no way to avoid a certain increase in consumption. But when it comes to frequently used sources – such as in break rooms and bathrooms – water isn’t left standing for long. As a result, the water usually reaches a constant temperature after a few seconds, at which point you can drink it without hesitation.
Why can’t we simply replace fixtures with models that don’t contain heavy metals?
Completely lead-free fixtures have not yet become standard. This makes them scarce and difficult to source. In addition, fittings, pipes and joints are built into walls, which means they can’t be easily replaced.
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