In 1945, the Food and Nutrition board advised that most people needed 2.5l of water/day, noting that most of this would come from your prepared foods.
This got garbled over the years into the theory that you needed to drink eight glasses of water every day. Which you totally, absolutely don't need to do. Even if you're drinking "diuretics" like coffee, which don't actually dehydrate you unless you're unadapted to caffeine.
There's no evidence that "staying hydrated" improves your skin, and the evidence for long-term health benefits from drinking a lot of water is pretty sketchy and inconclusive.
Note for Burners: while you need to drink a lot of water in the desert, if you're actually "pissing clear" consistently, you might be in danger of overhydration.
In other words, there’s very little reason to believe that children who have a spot urine measurement of 800 mOsm/kg should be worried. In fact, back in 2002, a study was published in the Journal of Pediatrics, one that was more exploratory in nature than a look for dehydration, and it found that boys in Germany had an average urine osmolality of 844 mOsm/kg. The third-to-last paragraph in the paper recounted a huge number of studies from all over the world finding average urine mOsm/kg in children ranging from 392 mOsm/kg in Kenya to 964 in Sweden.
That hasn’t stopped more recent studies from continuing to use the 800 mOsm/kg standard to declare huge numbers of children to be dehydrated. A 2012 study in the Annals of Nutrition and Metabolism used it to declare that almost two-thirds of French children weren’t getting enough water. Another in the journal Public Health Nutrition used it to declare that almost two-thirds of children in Los Angeles and New York City weren’t getting enough water. The first study was funded by Nestlé Waters; the second by Nestec, a Nestlé subsidiary.
It’s possible that there are children who need to be better hydrated. But at some point, we are at risk of calling an ordinary healthy condition a disease. When two-thirds of healthy children, year after year, are found to have a laboratory value that you are labeling “abnormal,” it may be the definition, and not their health, that is off.
No, You Do Not Have to Drink 8 Glasses of Water a Day [Aaron E. Carroll/NYT]
(Image: 02468370-65-Cracked Earth in St Thomas-1, Jim Sage, CC-BY)