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Boil-water notice: what to do when the tap water must be boiled

Updated · 5 min read

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After a cloudburst or flooding, tap water can become contaminated with, for example, coliform bacteria. The authorities then assess the risk and announce which precautions to take.[1] In Danish this is called a "kogeanbefaling" or "kogepåbud", and it doesn't mean you can't use the water. You just need to know when it must be boiled.

In short: The water you drink and cook with must be boiled, or you can use, for example, clean bottled water.[1] Always follow the authorities' instructions for your area.[1]

How you're told

In case of contamination, the municipality can order the waterworks to tell its customers that the water must be boiled.[2] The message can come in several ways, for example by text message, on the municipality's and the waterworks' websites, in local media and from loudspeaker vans.[2]

How to boil water properly

Boiling means heating the water to 100 °C for 1 minute, at a rolling boil. The water should then be cooled quickly in the fridge.[2] An ordinary kettle or saucepan works fine.[2]

  • Electric kettle: Boil the water twice, 2 to 5 minutes apart.[2]
  • Boiling-water tap: Water from kitchen taps with a built-in tank, typically kept at 108 °C, is sterile and needs no further boiling.[2]
  • Boil the water for 1 minute
  • Electric kettle: boil twice
  • Cool boiled water in the fridge
  • Or use clean bottled water

What can you use the water for?

The Danish Environmental Protection Agency lists what contaminated water can and can't be used for under a boil-water notice. The final assessment depends on the contamination, so follow your municipality's instructions.[2]

  • Drinking and cooking: Use boiled or bottled water.[1] You can boil pasta and potatoes in it, because boiling kills the microorganisms, but don't use it to rinse salad or other vegetables eaten raw. Rinse them in boiled water.[2]
  • Brushing teeth: Don't use contaminated water. Boiled water is fine.[2]
  • Bathing: The water can often be used for showers and baths, but make sure children don't drink it.[2]
  • Washing hands: You can wash your hands in it with soap if you dry them completely with a clean cloth or paper. Ideally disinfect afterwards with hand sanitiser containing 70 to 85% alcohol.[2]
  • Dishes: Washing up by hand needs boiled water. The dishwasher can be used on its hottest programme, heating the water to at least 70 °C.[2]
  • Laundry and floors: The water can be used, but kitchen counters and cupboards should be cleaned with boiled water.[2]

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If you fall ill

Watch out especially for diarrhoea, vomiting and fever after drinking contaminated water. Many stomach problems pass on their own within a couple of days, but if they continue or get worse, for example with blood in the stool or a fever, see a doctor.[1]

Food from a flooded basement

If food has been in contact with contaminated water, for example in a flooded basement, as a rule throw away food that isn't in watertight packaging. Tins and bottles can be used if you wash them thoroughly in clean water with disinfectant and rinse with clean water.[1]

Keep water in stock

This is where a home emergency kit makes a difference. Plan on 3 litres of water per person per day, so 9 litres per person for three days.[3] Read more about storage in emergency water.

Keep clean water ready

See how much drinking water the authorities recommend for your household.

See your checklist

For the full list of what to keep at home, read on here: Emergency supply list: what to keep at home

Frequently asked questions

How long should the water boil?

The water must be heated to 100 °C for 1 minute, at a rolling boil. With an electric kettle, boil the water twice, 2 to 5 minutes apart. Cool it quickly afterwards.

Can I brush my teeth with tap water?

No. Contaminated tap water must not be used for brushing teeth, but boiled water can be used.

Can I shower?

The contaminated water can often be used for showers and baths, but make sure children don't drink it. It depends on how contaminated the water is, so follow the authorities' instructions.

Can I use the dishwasher?

Yes, use the hottest programme so the water reaches at least 70 °C. Washing up by hand requires boiled water.

Sources

  1. [1]Danish Veterinary and Food Administration (Fødevarestyrelsen): Drikkevand forurenet med bakterier (in Danish)
  2. [2]Danish Environmental Protection Agency (Miljøstyrelsen): Kogevejledningen, guidance on microbiological drinking water limits (in Danish) (2026-07)
  3. [3]Danish Emergency Management Agency (Beredskabsstyrelsen): Prepared for crises

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