Everything from your mother to the food pyramid tells you to drink eight glasses of water per day in order to maintain a healthy level of hydration. But scientists are starting to believe that this recommendation might be a bit outdated. How much water should we really be drinking per day, and why?
The USGS, the government-sponsored educational forum, sticks to the old way of thinking, found in the 1945 Journal of Biological Chemistry. While researchers aren’t entirely sure where the daily water recommendations originated in literature, it’s rumored that its inception was in this very 1945 journal, still referenced by the US government today.
“The brain and heart,” the study begins, “are composed of 73% water, and the lungs are about 83% water.”
Skin is 64% water, muscles and kidneys are 79%, and bones even contain 31% water. So, to these scientists, it’s safe to say that we need to ingest a relative amount of water for these functions to operate well. And lucky for us, they did the math.
While the website notes that water consumption should “vary according to age and gender, and also by where someone lives,” they note that generally, for adults, a man needs to consume about 3 liters, and a female requires about 2.2 liters per day. But we don’t need to sit around chugging water all day to properly fulfill this requirement, as some foods contain water, as do all sorts of beverages.
This 2002 review in the American Journal of Physiology has a few things to say about this antiquated research, and the issue of “8 x 8” in particular.
“The seemingly ubiquitous admonition to “drink at least eight 8-oz glasses of water a day (with an accompanying reminder that beverages containing caffeine and alcohol do not count).”
There seems to be a lack of scientific review on this subject, and after both examination of “older literature that is not covered in electronic databases” and “extensive consultation with several nutritionists who specialize in the field of thirst and drinking fluids,” this 2002 study says.
The research now
The research on water consumption now is primarily fixated on one portion of the 1945 article: how much hydration varies between ages, sexes, sizes and living situations. Nutritionists seem to generally agree that for “healthy adults in a temperate environment leading a largely sedentary existence,” the 8×8 can be followed, but isn’t a complete necessity. The caffeine and alcohol exclusion has also been proven to be false, and in reasonable amounts, those two types of hydration count towards your larger intake.
The only reason one would drink more water is for either “the treatment or prevention of some diseases,” such as kidney disease, weight loss, or headaches, or “vigorous work and exercise, especially in hot climates.”
However, you might still be wondering: what’s the most honest answer about daily water consumption? The truth is that science has no idea. While water affects aging, thermoregulation, physical performance and mental performance, there have been limited studies on the ideal amount of water consumption, mostly because everyone’s size, shape, metabolism, and diet are so different. A 2011 report from the Nutritional Review reminds us that because so little research has been done with hydration, and there’s so much inconsistency in the physicality of the participants, the field of water research is a bit deserted.
The study continues explaining these mitigating variables. It estimates that for US citizens, about “22% of water comes from our food intake,” but it very much depends on one’s diet. In general, that number is much higher in countries like Greece or South Korea, which both have a higher intake of fruits and vegetables than Americans generally do. Foods like bananas, avocados, baked potatoes or cottage cheese contain 70%-79% water, while celery, lettuce, cantaloupe, spinach or pickles contain 90%-99% water.
Another variable is the size of the person who’s doing all the drinking. Heavier individuals, especially those who are obese, might be getting their “water intake” in the form of soups, sodas or sugary coffee drinks, so while they’re consuming a recommended amount of water, the excess sugar and sodium are creating a deficit in hydration. So, if you’re eating a pickle and expecting to feel quenched, remember that the salty brine will probably leave you feeling thirstier than before.
Where one lives is also an extenuating circumstance, as water is a cooling mechanism for the body to endure hot climates. So those living in a dry, cold state like Montana might not feel as parched as someone sweating their water weight away walking on a beach in the Florida summer sun.
While the 2011 study says that telling people how much water to drink might be a tricky business, science can’t recommend you stop trying to stay hydrated, as that will undoubtedly harm your health. The absence of water “will be lethal within days,” the study notes, so for the sake of potential kidney stones and brittle bones, try to stay hydrated, even if it’s not on an 8×8 schedule.
So what do I do?
Despite the lack of research, science has a pretty keen answer as to how to keep one’s hydration levels in check: just drink when you’re thirsty.
“Your body has a million years of evolution at play here when it comes to consuming water,” health tips website Eat This, Not That tells readers. “And it’s smarter at providing hydration instructions than any guideline or social-media challenge.”
So, while you might be thirstier depending on your activities or salt intake, you can trust your body to know when you need more water, or when you have enough.
However, you may find yourself in a circumstance where you don’t feel thirsty, but you’re dehydrated regardless. In that situation, you should examine the water that’s coming out of your body to know how much you should be putting in: if your urine is a light yellow color, that means you’re perfectly hydrated. Any darker, and you should refill your water bottle, or eat some celery.