Drinking-water contamination
Strictly follow an official boil order: boil water for drinking, cooking and teeth-brushing for at least 3 minutes at a rolling boil or use bottled water. Important – boiling only kills pathogens; if there is suspicion of chemical contamination, do not use tap water at all but switch to safe water from another source.
Drinking water can be contaminated by pathogens (e.g. E. coli, enterococci, Campylobacter, noroviruses) or by chemical substances. The most frequent triggers in Switzerland are heavy rain and floods, which wash debris and sewage into the catchment, as well as pipe defects and bursts. Because the water often only becomes noticeable once many people are already ill, contamination is insidious.
Safety is the responsibility of the water utility, the municipality and the cantonal laboratories or the cantonal chemist. If they detect a load, they issue a boil-water notice and inform the affected zone; it is only lifted once the water is demonstrably clean again.
Important to know: boiling reliably kills pathogens but does NOT help against chemical pollutants or heavy metals. In the case of chemical contamination, safe water from another source (bottled water, water tanker) is needed. How much water to keep in stock and how to treat it is shown in the guides "Treat drinking water" and "Build an emergency stockpile".
Risk rating
Likelihood: Medium · Impact: Medium → Overall risk: Medium.
| Impact | |||
|---|---|---|---|
| Low | Medium | High | |
| High | |||
| Medium | This hazard's rating | ||
| Low | |||
Legend: Low (green) · Medium (yellow) · High (red). Overall risk is likelihood multiplied by impact.
Pathogens or pollutants in tap water can make entire supply zones sick. When a boil-water notice is issued: boil the water or switch to safe water.
Immediate measures
- Strictly follow the official boil-water notice
- Bring water to a rolling boil or use bottled water
- If chemical contamination is suspected: do not use tap water at all
Warning signs
- Official boil-water notice from the water utility, municipality or canton
- Cloudy, discoloured water or an unusual smell/taste (foul, chemical)
- A cluster of gastrointestinal illnesses (diarrhoea, vomiting) in the neighbourhood
- A preceding flood, heavy rain or a burst pipe in the supply network
- Construction or repairs on the network followed by changed water
Before · During · After
Before
- Build a drinking-water stock (follow the federal recommendation)
- Know the treatment: boiling, filter, disinfectant (e.g. Micropur)
- Know the information channels of the local water utility/municipality
During
- Bring drinking/cooking water to a rolling boil for at least 3 minutes (all the more so at high altitude)
- Brush teeth and wash dishes with boiled or safe water too
- In the case of chemical contamination do NOT boil, but use safe water
- Follow the instructions of the water utility and authorities
- Prepare infant formula only with safe water
After
- Only stop boiling after the notice is officially lifted
- Flush taps and pipes thoroughly as instructed
- Seek medical help in case of persistent gastrointestinal symptoms
This really happened
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2022 Boil-water orders in Bernese municipalities
In summer 2022, after heavy rainfall, several municipalities in the Bernese Oberaargau (including Herzogenbuchsee) had to issue boil-water orders because of E. coli and enterococci found in the drinking water.
Source -
2019 Chlorothalonil in groundwater
In 2019 degradation products of the pesticide chlorothalonil were detected in groundwater nationwide, in many places above the maximum value of 0.1 µg/l. The FSVO classified them as health-relevant; the substance has been banned since 1 January 2020. Around 80 % of Swiss drinking water comes from groundwater.
Source -
2015 Norovirus outbreak via drinking water
An exceptional thunderstorm with around 60 mm of rain in 75 minutes led to drinking-water contamination with noroviruses; around 1194 people fell ill and five had to be hospitalised.
Source -
2008 Campylobacter outbreak via drinking water
A drinking-water-related Campylobacter jejuni outbreak in Switzerland caused around 185 illnesses; one person had to be hospitalised.
Source
Frequently asked questions
How do I prepare for drinking water contamination?
Keep a drinking water supply according to federal recommendations and learn about treatment: boiling, filtering and disinfectants such as Micropur. Familiarise yourself with your local water supplier's and municipality's information channels so you know about a boil order quickly.
Why doesn't boiling help against chemical contamination?
Boiling reliably kills pathogens such as E. coli, enterococci, Campylobacter and noroviruses. However, chemical pollutants and heavy metals are not removed – water evaporation can even concentrate them. In case of chemical suspicion, safe water from another source (bottled water, water tanker) is therefore necessary, not boiled tap water.
How do I know my drinking water might be contaminated?
The most important signal is an official boil order from supplier, municipality or canton. Other signs include turbid or discoloured water, unusual smell or taste, increased stomach-and-intestinal illnesses in the neighbourhood and preceding flooding, heavy rain or a pipe break in the network. Around 80 % of Swiss drinking water comes from groundwater.
Official sources
- SVGW Questions about drinking water
- FSVO Food and drinking-water safety
- Alertswiss Current notices