You get water from food as well, you know
It’s always puzzled me when people drink huge amounts of water. Whether it’s for ‘detox’ reasons, as part of a diet, or something else, it always seems to be tinged with a bit of moral showboating.
I do a fair amount of exercise. I drink water with some BCAA powder in it when I do. Other than that, I have a couple of cups of tea a day and water with my meals. Turns out, this is probably the right approach.
It is a common belief that you have to drink 6-8 glasses of water per day. Almost everyone has heard this recommendation at some point although if you were to ask someone why you need to drink this much water every day, they probably wouldn’t be able to tell you. There is usually some vague idea that you need to drink water to flush toxins out of your system. Perhaps someone will suggest that drinking water is good for your kidneys since they filter the blood and regulate water balance. Unfortunately, none of these ideas is quite true and the 6-8 glasses myth comes from a fundamental misunderstanding of some basic physiology.
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You will always lose water vapour in your breath, provided you keep breathing, and you will always produce… watery-odour free sweat even if you move to the Arctic. Of course, if you move to the tropics you will produce much more sweat to compensate for the extra heat. But all told, roughly 1.5-2 litres of water loss are obligatory losses that we cannot do anything about. Those who exercise, live in hot climates or have a fever will obviously lose more water because of more sweating. Thus, a human being needs to replenish the roughly 2 litres of water they lose every day from sweating, breathing, and urination. The actual notion of 8 glasses a day originates from a 1945 US Food and Nutrition Board which recommended 2.5 litres of daily water intake. But what is generally forgotten from this recommendation is, firstly, that it was not based on any research and that secondly the recommendation stated that most of the water intake could come from food sources.
All food has some water in it, although obviously fresh juicy fruits will have more than, say, a box of raisins. Suffice it to say that by eating regular food and having coffee, juice or what have you, you will end up consuming 2 litres of water without having to go seek it out specifically. If you find yourself in a water deficit, your body has a very simple mechanism for letting you know. Put simply, you will get thirsty.
If you are thirsty, drink water. If you are not thirsty, then you do not need to go out and purposefully drink 6-8 glasses of water a day since you will probably get all the water in your regular diet. One important caveat to remember though is that on hot summer days, your water losses from sweating go up and if you plan to spend some time out doors, having water with you is important to avoid dehydration and heat stroke. While the thirst reflex is pretty reliable, it does tend to fade with age and older people are more likely to become dehydrated without realizing it. Thus, the take home message is drink water when you are thirsty, but on very hot days it might not be a bad idea to stay ahead of the curve and keep hydrated.