Boil-water notices and water during floods

Tap water is normally one of the most closely monitored foods. The pipe network is kept under pressure so that nothing gets sucked in from outside. If a main bursts, pressure drops or flood water enters wells and treatment plants, germs from soil or sewage can get into the network. If germs are found, or even just feared, the authority issues a boil-water notice.

Boiling works through heat: bacteria, viruses and parasites such as Giardia cannot survive water at a rolling boil and are made harmless. What matters is a real, vigorous boil, not just warm water or a few bubbles at the bottom of the pot. At high altitude water boils at a lower temperature; there the authorities recommend boiling for longer.

Chemicals, fuels, heavy metals or salts, on the other hand, are not destroyed by heat. When water boils only the water itself evaporates; the dissolved substance stays behind and becomes more concentrated. That is exactly why there are two different kinds of notice – and why the type of notice is the most important piece of information of all.

Under a boil-water notice a simple rule applies: everything that goes into the mouth needs boiled or bottled water. That includes not only drinks but also brushing teeth, ice cubes, infant formula, cooking and washing fruit and vegetables that are eaten raw. Brushing teeth in particular is often forgotten because it is a habit.

A fixed routine helps: in the morning, bring a large pot of water to a rolling boil, let it cool covered and pour it into clean, labelled bottles or jugs. A note on the tap reminds everyone in the household that nobody drinks from the tap right now. Throw away ice cubes made before or during the notice.

When the notice is lifted, the job is not quite finished. The utility usually says how long the pipes should be flushed. Filter cartridges in fridges or jug filters may have picked up germs and are replaced according to the manufacturer. Appliances with a water connection are also treated as the authority advises.

During a flood, sewers, treatment basins, heating-oil tanks, cars and garages fill with water. The water that then flows through streets and cellars is therefore almost always a mixture of sewage, mud, fuel and chemicals. You cannot see what is in it, and no household method makes it safe to drink.

So the rule is: do not drink flood water, avoid contact as far as possible and wash your hands thoroughly after touching it. Food, drinks and containers that were in flood water are thrown away or cleaned as the authority says. Even sealed bottles can be dirty on the outside, especially around the cap.

A private well in a flooded area counts as contaminated until it has been tested or disinfected as instructed. Until then, use bottled water or water from official distribution points.

The biggest danger is a mix-up: anyone who boils water under a ‘do not drink’ notice feels safe and may drink a concentrated mixture. So always read the exact wording of the notice and check via official channels such as a warning app, the radio or the utility's website which area it covers.

Boiling water causes severe scalds. Turn pot handles inwards, keep children away from the stove and hot pots, and let the water cool completely before pouring it into other containers. Special rules apply to infant formula; here, follow the guidance of the authority and the paediatrician.

Showering and handwashing are usually allowed under a boil-water notice, as long as no water is swallowed – go by what the authority says. Give small children short baths under supervision so they do not drink bath water. Anyone who develops diarrhoea, vomiting or fever drinks plenty of safe water and seeks medical help for severe symptoms; in an emergency call the local emergency number (112 in the EU).

Boil-water notices are among the most common measures worldwide when water supply is disrupted, and they are usually temporary. They do not mean the water looks dirty – it can be perfectly clear and still contain germs.

If electricity or gas fail and you cannot boil, use bottled water or the chemical disinfection the authority explicitly names. A small stock of bottled water at home takes a lot of the stress out of such situations.