Water. H2O. Dihydrogen Monoxide. Whatever you call it, we all know of the importance of water. In fact, water is so important it is literally one of the foundational requirements of human life. Those foundational elements are:
We live on a blue planet. All life as we know it requires ample water to survive. Go without water and you’ll die within a few days. The human body consists of ~60% water (1).
You're basal metabolic rate (BMR) determines the amount of calories you need to function day to day. Dip below that and you will lose weight as mostly fat and some lean tissue stores are utilized for energy. Carry that starvation mode out to the extreme, and 1,200 calories per day is the amount needed just to live. Of course vitamins, minerals, and more are all required too!
Humans require an oxygen percentage of 19.5 - 23.5%. Go less than 19.5% and death will quickly occur, within minutes. Go above 23.5% and death will eventually occur, though more slowly, over the course of hours.
Don’t believe me? In a study out of Russia, infants left alone in their cribs with minimal or no physical contact from the care providers suffered severe delays in physical growth, neurobehavioral development, and had elevated rates of serious infections. More than a third died (2).
Skip out on sleep for days on end and you risk an early grave. No studies have been done yet to quantify exactly how long it takes sleep deprivation to kill humans, but studies have been done on rats and dogs, with fatal consequences.
I bring up those five requirements for human life because I want to make clear how important each one of them is, especially water. Going throughout life, it should always be a priority to make sure those elements of life are not found lacking or deficient in any way. If they are deficient, how can you aspire to tackle tasks larger in scope?
With that in mind, it blows me away when people stay in a near chronic state of dehydration. From poor people, a situation where it is objectively harder to stay hydrated, to rich folks, whose access to resources and money should make acquiring adequate water easy, people from all walks of life have yet to learn the value and importance of water.
One Chemical, Thousands of Uses
From making up the majority of your blood to being critical for digestion, water is required for thousands of different purposes and metabolic processes throughout the body. Each of these processes is ranked in importance too depending on the current situation you’re in (such as high heat or excess stress) and the speed of which it will kill you if stopped (i.e. no more water). It is this constantly shifting network of functions that water is used to maintain, and depending on the situation, your body will best partion and utilize the water it has available towards the most pressing issues. It is for this reason that it is so important to make sure you’re never dehydrated day to day*.
*Note - As always, caveats apply. Occasional dry fasting is likely a beneficial acute stressor, helping to build resilience and increase water use efficiency throughout the body.
Dehydration Affects Mental and Physical Performance
By placing your body in a state of dehydration, you are placing yourself in a state of stress, the severity of which is determined by your level of dehydration. For example, it’s been shown that rehydrating after a 12 hour zero water dry fast positively affects mood and cognitive performance on a variety of tasks that assess memory, attention, executive function, and speeded responses compared to the dehydrated state (3). As for physical performance, both endurance and strength activities are affected by dehydration.
For long duration aerobic exercise, such as running or cycling, performance begins to decrease when the level of dehydration exceeds 2-3 percent body weight loss (4). Strength training is affected too, with anaerobic performance being observed to significantly decrease around 3-4 percent body weight loss (5).
In one study, when seven subjects were critically dehydrated, the severity of their fatigue during exercise increased by over 70%! Meanwhile, mean and peak power output was decreased 7% & 14.5% for the upper body and 19% & 18% for the lower body (6).
Drink Water and Thrive
Without delving too deep, it is clear that water is instrumental in maintaining a healthy body and mind (7). And not just water, but a surplus of water. Just as a car needs oil and lubricants to run smoothly, the human body requires water to likewise function smoothly.
If you’re unsure of how much water to drink , use the simple formula below to calculate a good daily water intake to start with. Experiment with your daily water intake and find the amount that is optimal for you!
Optimal Daily Water Intake (oz) = Body-weight (lbs) x 0.75 oz water
1 gallon = 128 oz | 1 liter = 33.8 oz
Body-weight 125 lbs = 94 oz
Body-weight 150 lbs = 112 oz
Body-weight 175 lbs = 130 oz
Body-weight 200 lbs = 150 oz
Body-weight 225 lbs = 168 oz
Body-weight 250 lbs = 188 oz
Mitchell HH, Hamilton TS, Steggerda FR, Bean HW. The Chemical Composition of the Adult Human Body and Its Bearing on the Biochemistry of Growth. Division Animal Nutrition, University of Illinois, Urbana. 1945.
Albers LH, Johnson DE, Hostetter MK, Iverson S, Miller LC. Health of children adopted from the former Soviet Union and Eastern Europe. Comparison with preadoptive medical records. JAMA. 1997;278(11):922-4.
Patsalos OC, Thoma V. Water supplementation after dehydration improves judgment and decision-making performance. Psychol Res. 2019;
Bardis CN, Kavouras SA, Arnaoutis G, Panagiotakos DB, Sidossis LS. Mild dehydration and cycling performance during 5-kilometer hill climbing. J Athl Train. 2013;48(6):741-7.
Kraft JA, Green JM, Bishop PA, Richardson MT, Neggers YH, Leeper JD. The influence of hydration on anaerobic performance: a review. Res Q Exerc Sport. 2012;83(2):282-92.
Jones LC, Cleary MA, Lopez RM, Zuri RE, Lopez R. Active dehydration impairs upper and lower body anaerobic muscular power. J Strength Cond Res. 2008;22(2):455-63.
Popkin BM, D'anci KE, Rosenberg IH. Water, hydration, and health. Nutr Rev. 2010;68(8):439-58.