Pale yellow

About this video

A friend carries a big bottle everywhere and says you must drink eight glasses of water a day or you will dry out. How much do you really need?

Your body loses water all day: in pee, in sweat and in every breath you breathe out. Hydration means having enough water to replace what it loses; dehydration is when the body loses more than it takes in. The NHS lists the early signs: feeling thirsty, dark yellow and strong-smelling pee, peeing less often than usual, a dry mouth, a headache, and feeling tired or dizzy. Babies, children and older adults get dehydrated more easily.

The European Food Safety Authority says about 2.0 litres of water a day is enough for women and about 2.5 litres for men, from drinks and food together; part of it comes from fruit, vegetables, soup and yoghurt. The NHS gives 6 to 8 cups or glasses of fluid a day as a guide, and water, lower-fat milk, tea and coffee all count. You need more when it is hot, when you are active for a long time, and when you are ill.

"Eight glasses a day" is a handy guide, not a scientific rule: in 2002 the kidney scientist Heinz Valtin looked for the studies behind it and found none. For healthy people, thirst is a good guide, since the body starts to feel thirsty long before it is in trouble. And there is a simple check anyone can do: pale yellow pee is a good sign you are drinking enough, while dark yellow means drink more.

Drinking far more than the body loses, quickly, can lower the sodium in the blood, which can be dangerous. It is rare, and mostly happens in long sports events: at the 2002 Boston Marathon, about 1 in 8 runners tested at the finish had low sodium in their blood, and the runners most at risk had gained weight during the race, because they drank more than they sweated out. This video explains hydration, from the lesson How Much Water? on Knaph.

Transcript

1. 0:00Your friend says you must drink eight glasses a day, or you'll dry out. Really?
2. 0:06The body loses water all day, in pee, sweat and breath. Hydration is having enough to replace it. Dehydration is losing more than you take in.
3. 0:17Early signs are thirst, dark strong-smelling pee, peeing less, a dry mouth, a headache, and feeling tired or dizzy. Children and older adults get there more easily.
4. 0:31About two litres a day for women and two and a half for men, from drinks and food together. The NHS guide is six to eight glasses. Water, milk, tea and coffee all count. More when it's hot, when you're active, or ill.
5. 0:50Exactly eight? A kidney scientist looked for the studies behind it and found none. For healthy people, thirst is a good guide.
6. 1:01And there's a simple check. Pale yellow pee means you're drinking enough. Dark yellow means drink more.
7. 1:11Too much, too fast, can lower the sodium in your blood. In the 2002 Boston Marathon, about one in eight runners tested had low sodium. Most at risk were those who gained weight, drinking more than they sweated.
8. 1:26Drink when you're thirsty. Aim for pale yellow.