Emergency water from the water heater and pipes

A water heater tank is a large, closed container. Depending on its size, it holds a considerable amount of water. At the top, hot water flows to the taps; at the bottom there is usually a drain valve. For water to run out at the bottom, air must be able to enter at the top – otherwise a vacuum forms and the water stays in. You know this from a drink carton: without an air hole, hardly anything comes out.

So you close the cold-water inlet, open a hot tap above to let air in and drain the water from the drain valve. The pipes work in a similar way: you open the highest tap in the house to let air in and catch the water at the lowest tap in clean containers.

The water is only as clean as the tap water was before the failure. If the supply may already have been contaminated, it must be boiled or disinfected according to official instructions before drinking.

Risk of scalding: the water in the tank can be very hot. Let it cool before you open the drain valve, and keep children away.

Appliance safety: before draining, switch off power or gas to the water heater as described in its manual. Switch it on again only once the tank is completely full and vented. A tank heated while empty can be damaged or cause a fire. Restart gas appliances only as the manufacturer instructs, or have professionals do it. Work on electrical or gas installations belongs in the hands of professionals.

Water from radiators and heating systems is not drinking water, as it often contains additives. Toilet bowls and cisterns, waterbeds, pools and hot tubs are also off-limits. If there is a warning that the mains is contaminated, for example after a burst main or flooding, close the main shut-off valve where the authority advises this – so that no contaminated water flows into pipes and tank.

The first water from the tank may contain sediment, such as limescale or rust. Catch it in a separate container, let it settle and then scoop off the clear water at the top. You do not drink the sediment at the bottom.

Not every installation has a tank. Tankless heaters only heat water as it flows through and hold hardly any water. Installations in rented flats or apartment buildings are also often central and not easily accessible – in that case, talk to the building management beforehand if possible.

Ice cubes made from clean tap water and frozen water bottles are a simple, safe reserve. Let them thaw in a clean container.

In an emergency it is dark, hectic and possibly without power. That is why it pays to get to know your own installation calmly: where is the main shut-off valve? Where is the water heater, where is its drain valve, and how is it switched off according to the manual? Which is the highest and which the lowest tap in the house?

Keep the heater’s manual within reach, have a headlamp ready for the basement and a few clean, food-grade containers. Mark the main valve clearly so other household members can find it too. That way you can act calmly and step by step in an emergency.

Once the supply is restored, the most important rule applies: fill first, then heat. The tank is filled completely and vented before power or gas is switched back on.

Official preparedness guides in the United States explicitly name water heaters, pipes and ice cubes as “hidden” water sources in the home. At the same time they warn against heating systems, toilets, waterbeds and pools.

These reserves are limited and do not replace your own drinking-water stock. But they can help bridge the first days of a disruption until the authorities supply water or the supply runs safely again. Domestic installations differ greatly – if you know yours, you have a clear advantage.