Britain faced the hottest day ever recorded in July on 19th of July as a heat wave swept much of Europe. Temperatures hit 96.6 degrees south of London — so hot some road surfaces melted. There was little London officials could do besides tell people to carry a bottle of water.

Elderly people are most vulnerable because they don’t drink enough water, which lowers blood pressure overall. When it’s this hot, we lose about a litre of water a day just by sweating. People should be drinking at least 2-3 litres of water each day.

70,000 residents were urged to cut water use in Shrewsbury while in Nottinghamshire, Derbyshire and Cardiff water supplies were affected.

The water saving was particularly noticeable on hotter days. Duncan McCombie, Thames Water customer service manager, said. "We want to say a big thank-you to all our customers who have been saving water during the drought, but with July temperatures soaring we do very much need them to keep up the good work.

Across Europe, officials warned citizens to stay out of the sun and drink plenty of water.

The hot weather — up to 97 degrees in Paris on Wednesday — recalled the record-breaking 2003 heat wave that left 15,000 people in France dead of dehydration and other problems.

In France, advice was broadcast day and night on radio and television with reminders to drink water and stay indoors. Drinking water was essential on a day when dehydration was a legitimate concern for anyone outside.

The key word in discussing dehydration is water. To dehydrate means 'to remove water.' Dehydration occurs when more body fluid is lost than taken in. Sixty percent of total body weight comes from water. The body cannot function without water.