The ability to hydrate our cells transcends nearly any other somatic control and choice we make as humans. Though our bodies are comprised of nearly 60% water, it does not neglect the fact that it’s basic chemistry will still follow the laws that pertain to gradients; molecules will flow from areas of high concentration to those of low concentration, attempting to create an equilibrium. This then makes it challenging for the body to be at homeostasis as a (lower, but even) equilibrium across all areas of needed-hydration may not be optimal for any one specific tissue or cell.

According to H.H. Mitchell, Journal of Biological Chemistry 158, the brain and heart are composed of 73% water, and the lungs are about 83% water. The skin contains 64% water, muscles and kidneys are 79%, and even the bones are watery: 31%. - USGS Water Science School

With the human body being made mostly of water, the percentage of which will determine how well we are able to perform throughout the day, on both a cellular and activity level. This percentage can be found by dividing your total body water (TBW) by your body weight (BWT);

TBW/BWT = % of water

This can further be examined by looking at percentages of intracellular vs extracellular fluids (if access to certain technologies allows). An ideal environment for your cells would be 2/3 of fluids as intracellular (inside the cell, mostly cytoplasm) and the other 1/3 pertaining to your extracellular water (lymph, blood, cerebrospinal fluid). Like most things in chemistry, water will follow a pressure gradient, it will seek to polarize from higher concentrations and pressure to lower ones, often following sodium (Na+), as it wants to dilute solutions that have high concentrations of X molecules. The need for water ranges from basic homeostatic controls of the body like core body temperature to development and survival components as well as a basis for all cells to interact in as it is chemically one of the best buffers available (buffer essentially not affecting the innate pH of any chemical that is put in it). For blood, we know the water makes up roughly 92% of it and this not only affects the viscosity of it but also its ability to move molecules through the circulatory system. If you’re dehydrated or somewhat constantly dehydrated, you’re making your left ventricle (of the heart) work harder than it has to, which on a performance level is already not doing yourself any favors.

On one side of it, we have water soluble vitamins and minerals being delivered to tissues; vitamin B and C as an example bind to H2O molecules can either passively diffuse (simple diffusion) into cells or be transported via aquaporins pending the type membrane (often, but not exclusive to a lipid bilayer that helps differentiate the content of the cell from its external environment). For elimination we can think of any water soluble hormones or toxins (such as heavy metals) that need to be excreted from the cell/body (via urine or sweat). An interesting component here is to think about what happens when we are dehydrated on a more frequent basis. This can lead to increases of circulating cholesterols as cells will attempts to increase their rigidity by placing more and more cholesterol into their lipid bilayer (membrane of our cells) to prevent more intracellular fluids from being lost. This becomes problematic in a couple of areas. More rigidity prevents smooth movement of cells thru vessels and less permeability of the cell may have prevent waste products from inside to leave, and nutrients outside of it that is required to enter the cell enable to penetrate the membrane as cholesterol tightens up these ‘walls.' In general if extracellular fluid (blood plasma, lymph, intravascular fluid and cerebrospinal fluids) is low (creating a higher saturation of solutes), and cell hydration is higher (solution is more desaturated), then following the principles of gradients, the intercellular water will ‘attempt to leave the cell’ — dehydrating it.

So how does someone become dehydrated? It may actually be easier than you would think. Losing water via sweat is one of the most common ways that our water levels can be offset; this is dependent on  but not limited to factors such as geography (heat), activity level, and thyroid function. Components of training, nourishment and lifestyle are highly individualized, and for that reason, taking in consideration the individuality of the athlete, water loss and ability to hydrate are just the same. Hormonal balance, electrolyte status, carb/fiber intake, bowel formation are all components here. Someone who leans more towards a type 7 on the Bristol stool chart will be losing more water through elimination and will need to make up for it to maintain a better state. Carbohydrates (including fiber) have a binding tendency that tends to pull a lot of water due to its steric structure as a molecule — this directly impacts how much water will be pulled through the lumen. Paradoxically, if we drink too much water (and/or too fast), we will oversaturate our blood plasma levels (with water) and the kidneys will start the process of filtering water out get our viscosity back to a level that is closer to homeostasis (and also losing minerals in the process). Chronic over-hydration or ‘water intoxication’ can lead to imbalances in electrolytes (minerals). The human body is more or less a closed system, our cells can arguably take more water at certain points, however the circulatory system needs a homeostasis, and with sodium being water soluble, when excess water is eliminated via urine, we also lose sodium throwing off our electrolyte gradient for extracellular fluid levels. This occurs similar to having high blood pressure, with chronic high BP, our GFR is up-regulated and more urine is created but at the cost of a decrease ability for reabsorption (of wanted molecules such as Na+, Cl-, K+); further further lead to symptoms of hyponatremia (low Na+ levels).

Adults can range between 47 and 61% pending their age and sex. A 70kg man with 60% hydration would be holding roughly 42 liters/water. Typically due to the hormone-based need for essential fat (cells), adult women tend to have lower counts of water as adipocytes contain far less water than other cells; in athletic populations that may be skewed closer to male percentages as women will tend to hold less body fat pending the specificity of sport.

Tips for Athletes

1.    Primary goal: Pee as little as possible while still staying fully hydrated. This will not only keep your electrolyte balance on point but also ensure that your nervous system and kidneys are not working any harder than they have to.

2.    If you sweat a lot and/or you are prone to dehydrating, weigh yourself before and after training sessions. 1 lb lost is equal to 15.3 oz of water; you’ll be losing water throughout the day by other means (urine, feces, respiration, talking) but at least you’ll have a jump on getting yourself back to a where you were before training.

3.    Be conscious of your minerals; Whether you eat super clean or bulk of your calories come from highly processed supplementation, you may be lacking your minerals do to the above stated; ensure your sodium, potassium (and calcium for that matter) are at least on the point with the RDA recommendation as a starting point. You can do this by adding trace minerals to your water or throwing a tsp of of quality sea salt in your AM water to start your day.

4.    Sipping > Chugging. A slow steady increase of water will help provide your body with the proper hydration with less risk of having to pee in excess.

5.    Your first task of the day is to rehydrate; 8hrs of respiration will cost you some water. Support your cellular energy needs, nervous and circulatory systems and work on getting 12-16 oz of water in ASAP, while still following tip #4.

There is a silent dehydrated that not many folks think about, and it ties in directly to different vocations. Both talking and breathing for that matter, has water vapor in it, the average human will expire 5 mL/min of oxygen, and with that will come a 400 mL of water/day. Folks that talk sales or coach for a living and talk constantly throughout the day will need to likely take in more than their doppleganger. Renal, cardiovascular, sympathetic and endocrine systems are all highly regulated by hydration and your kidneys ability to regulate homeostasis between reabsorption and excretion. Without which, neurological components from coordination to muscle contractions and the ability to move substrates to the cell and byproducts from the cell will be compromised. With our bodies being run on an electrochemical gradient, having an ability to drive anions (negatively charged ions) it becomes an extremely beneficial component of your nourishment to manage.