Heatwave and Power Cut: How to Keep Your Household Safe

Quick answer: In a heatwave, keep the sun out by day, let cooler air in at night, drink regularly and check on anyone vulnerable. Store at least 1 US gallon (about 3.8 litres) of water per person per day, and plan for more, because Ready.gov says water needs can double in very hot weather. Most medicines should stay below 25°C, and fridge medicines such as insulin need a plan for when the power goes off.

Heat is a quiet emergency, but health agencies treat severe heat as a risk to life. When it also pushes the power grid too far, fans, fridges and air conditioning stop at exactly the wrong moment. Here is what recent outages show and what official health advice says you can do at home.

When heat and power cuts arrive together

Heat raises electricity demand, because so many people switch on cooling at once. It can also strain the equipment that delivers power. Recent examples show how this plays out:

June–July 2025, Europe. Energy think tank Ember found the heatwave raised daily electricity demand by up to 14% in Spain and 9% in France. At least 7 GW of French nuclear capacity was forced offline on 1–2 July because river water was too warm for cooling.
January 2025, Argentina. During a heatwave with temperatures near 40°C, outages hit Rosario and Greater Buenos Aires, where up to 71,800 homes lost power at the peak. The Buenos Aires Herald reported that the cuts also disrupted water supply in both cities.
23 June 2026, France. A transformer failure linked to extreme temperatures near Quimper in Brittany left about 68,000 households without electricity, during a heatwave when 58 French departments were on red heat alert.
21 August 2026, Cyprus. With temperatures around 40°C in the capital, a grid failure at peak demand cut power across large parts of the island, including Limassol District and the suburbs of Nicosia.

Not every heatwave causes blackouts, but the pattern is clear enough to plan for. Note the Argentina case: a power cut can also disrupt your tap water.

What the warnings mean

Many countries now run heat-health warning systems. In England, the UK Health Security Agency (UKHSA) issues colour-coded heat-health alerts. A red alert means a severe heatwave could affect transport, food, water, energy supplies and businesses, and that there is a risk to life even for healthy people. UKHSA issued a red alert for six regions of England from 24 to 26 June 2026.

Wherever you live, sign up for your national weather and heat warnings, and treat the top level as a signal to act, not just to take note.

Keeping cool when the power is off

The advice from the WHO, UKHSA, the US CDC and Ready.gov is very consistent:

Block the sun. Close blinds, curtains or shutters on windows that get the sun during the day. Ready.gov also suggests weather-stripping doors and windows.
Use the night. Open windows when the air outside feels cooler than inside, usually at night and early morning, if it is safe to do so.
Cool your body. Take cool showers or baths, or use a wet cloth, cold packs or a foot bath. Wear light, loose, light-coloured clothing.
Cut indoor heat. Switch off lights and electrical devices you are not using.
Slow down. Avoid hard physical work in the hottest part of the day. UKHSA’s alerts point to 11am–3pm as the time to stay out of the sun.
Find a cool place. The WHO suggests spending 2–3 hours a day somewhere cool, such as an air-conditioned public building, if your home cannot be kept cool. Know where your nearest cooling centre, library or shopping centre is before you need it.

About fans: UKHSA says electric fans can help when the temperature is below 35°C, but you should not point them straight at your body. Ready.gov warns against relying on a fan as your main way of keeping cool. A battery or USB fan with a charged power bank is useful in an outage, but it is not a substitute for a cool place in extreme heat.

Never leave children, older people or pets in a parked car, even briefly. Our power outage guide covers lighting, food in the fridge and safe backup power.

How much water to store for hot weather

Ready.gov and the CDC recommend at least 1 US gallon (about 3.8 litres) per person per day, for drinking and basic hygiene. Ready.gov adds that water needs can double in very hot temperatures, and that children, nursing mothers and sick people may need more. The CDC suggests at least 3 days, with 2 weeks as the goal.

Household	3 days, normal weather	3 days, very hot weather
1 person	about 11 litres (3 US gal)	about 23 litres (6 US gal)
2 people	about 23 litres (6 US gal)	about 45 litres (12 US gal)
4 people	about 45 litres (12 US gal)	about 91 litres (24 US gal)

Add extra for pets. Drink regularly through the day rather than waiting until you feel thirsty. UKHSA says pale, straw-coloured urine is a good sign you are drinking enough. Water and diluted squash are best; the WHO advises avoiding sugary, alcoholic and caffeinated drinks. Ready.gov says never ration drinking water unless the authorities tell you to.

For containers and rotation, see how much water to store.

Who is most at risk

UKHSA lists people at higher risk as including:

people aged 65 and over, and children under 5
people with heart or breathing problems, dementia, diabetes, kidney disease or Parkinson’s disease
pregnant women, and people taking certain medicines
people with serious mental health conditions
people who live alone, work outside or are homeless

The CDC warns that power failures in hot weather can be deadly, and asks people to check on neighbours and relatives who may need help. Agree now who will call or visit whom during a heatwave.

Heat-sensitive medicines

The UK medicines regulator (MHRA) issued heat advice on 10 July 2025. It said most medicines should be stored below 25°C, away from hot cars, bags and sunny windowsills. Insulin and some liquid antibiotics need a fridge and are especially vulnerable to heat. Inhalers can also be damaged.

If a medicine looks different, such as a change in colour, smell or texture, ask a pharmacist before using it.
Diuretics (water tablets) and some blood pressure medicines can raise the risk of dehydration or make it harder for your body to control its temperature. Do not stop them; ask your doctor or pharmacist for advice.
Blood glucose monitors may give less reliable readings when used or stored in heat.

For insulin, the US Food and Drug Administration (FDA) says vials and cartridges can usually be kept unrefrigerated between 15°C and 30°C (59–86°F) for up to 28 days, depending on the product. In an emergency, keep insulin as cool as possible but never let it freeze, and do not use insulin that has frozen. The CDC notes you may have to use insulin that got warmer than 30°C during an emergency; check your blood sugar closely and replace it once you can. Our guide to medications in emergencies explains how to build a small reserve with your doctor.

Know the danger signs

UKHSA describes heat exhaustion as tiredness, weakness, feeling faint, headache, cramps, nausea, heavy sweating and intense thirst. Move the person somewhere cool or shaded, remove extra clothing, give cool drinks, and spray or sponge their skin with cool water; cold packs wrapped in a cloth under the armpits or on the neck also help. UKHSA says heat exhaustion does not usually need emergency care if the person cools down within 30 minutes.

Heatstroke is a medical emergency. Signs include confusion, poor coordination, a fast heartbeat or breathing, hot skin that is not sweating, and seizures. Call your emergency number (999 in the UK, 911 in the US, 112 in the EU) and cool the person while you wait.

Your heatwave and power cut checklist

Heat and weather warnings switched on for your area
Water for at least 3 days, doubled for very hot weather
Blinds, curtains or reflective window covers for sunny windows
Battery or USB fan, power bank and spare batteries
Cool packs, flannels and a spray bottle
A cool spot for medicines, and a plan for fridge medicines
Nearest cooling centre or cool public building noted
A list of people to check on, and who checks on you
Battery lantern and torch for night-time outages

Want to see how your stores would hold up? See how many days your household would last with the free calculator. During any heatwave, follow your national health agency and local authorities.

Sources & further reading

Every fact in this post was checked against the sources listed above on 1 November 2026. Advice changes: always follow your local authorities.