Hydration: The Basics

What Is Hydration?

You've heard it a thousand times: drink more water. But why does hydration matter so much? The answer lies in your biology. Roughly two-thirds of the human body is composed of water; it's the primary ingredient in every bodily fluid you produce including saliva, blood, urine, sweat, and joint fluid. Without an adequate supply of water, virtually every system in your body begins to struggle.

Hydration simply means maintaining the right amount of water in your body to keep these systems functioning properly. It's not just about gulping down eight glasses a day, it's about understanding the balance between how much water you take in and how much you lose throughout the day.

What Causes Dehydration?

Dehydration occurs when your body loses more water than it takes in. But it's not always as simple as forgetting to drink enough. Several factors influence how quickly you lose water and how much you actually need to consume to stay balanced.

Strenuous Activity

Exercise and physical labor cause you to sweat, sometimes significantly. Sweat is your body's cooling mechanism, but it comes at a cost: water, electrolytes, and other micronutrients are lost with every drop. The harder and longer you work out, the more you'll need to replenish. Athletes and people who work physical jobs need to be especially mindful of fluid intake before, during, and after exertion.

Hot Weather

Warm and humid environments accelerate sweating even without physical exertion. On a hot summer day, you can lose a surprising amount of water simply by existing outdoors. If you're both active and in the heat, your hydration needs multiply quickly.

Illness

Being sick taxes your body's fluid reserves in multiple ways. Common illness symptoms such as: fever, sweating, vomiting, diarrhea, coughing, and increased mucus production all expel water from the body at a faster than normal rate. This is why staying hydrated is one of the most repeated pieces of advice when you're under the weather. Your body is working overtime, and it needs the resources to do so.

Signs of Dehydration

How do you know when you're not getting enough water? Dehydration exists on a spectrum, and the symptoms range from mild to medical emergencies.

Minor Symptoms

•       Thirst — your body's first warning signal. By the time you feel thirsty, you're already mildly dehydrated.

•       Dark urine — pale yellow is the goal; dark yellow is a sign to drink up.

•       Headaches — dehydration can cause blood vessels to narrow and trigger tension headaches.

•       Fatigue and reduced concentration — even mild dehydration can sap your energy and mental sharpness.

•       Dry mouth and bad breath — reduced saliva production is a hallmark of dehydration.

Major Symptoms

•       Dizziness and fainting — especially when standing up quickly (orthostatic hypotension).

•       Rapid heartbeat and rapid breathing — the heart works harder when blood volume drops.

•       Sunken eyes and dry, shriveled skin — visible signs of significant fluid deficit.

•       Confusion and irritability — the brain is highly sensitive to fluid changes.

•       Little or no urine output - dark amber or brown means you need to drink water urgently.

•       Muscle cramps — electrolyte imbalances from dehydration can trigger involuntary muscle spasms.

Severe dehydration is a medical emergency. If you or someone else is confused, fainting, or not urinating, seek medical attention immediately.

The Role of Electrolytes

Water alone isn't always enough. Your body also depends on specific nutrients, particularly electrolytes, to use that water effectively. Without the right balance of these compounds, your cells can't properly absorb and retain fluids, no matter how much you drink.

What Are Electrolytes?

Electrolytes are substances that carry an electrical charge when dissolved in water or body fluids. This charge allows them to regulate chemical reactions and maintain the fluid balance between the inside and outside of your cells.

According to the National Cancer Institute, they help move nutrients into cells, move waste out of cells, and support the proper functioning of nerves, muscles, the heart, and the brain.

A Quick Chemistry Lesson: What Is a Salt?

You might be surprised to learn that "electrolyte" and "salt" are closely related concepts, but are not interchangeable. In chemistry, a salt is an ionic compound formed when an acid and a base neutralize each other — the result is a positively charged ion bonded to a negatively charged ion.

The most familiar example is table salt, or NaCl (sodium chloride). When dissolved in water, the ionic bond between sodium (Na⁺) and chloride (Cl⁻) breaks apart, freeing both ions to move through the fluid. These ions are electrolytes — and they're just two of many.

Other common edible salts you may encounter include:

•       KCl (Potassium Chloride) — a sodium substitute found in some salt alternatives

•       MSG (Monosodium Glutamate) — a flavor enhancer common in Asian cuisines

•       MgCl (Magnesium Chloride) — used in supplements and food production

•       CaCl₂ (Calcium Chloride) — used as a preservative and firming agent

•       NaHCO₃ (Baking Soda) — sodium bicarbonate, used in baking and antacids

•       CaCO₃ (Calcium Carbonate) — found in antacids and calcium supplements

It's worth noting that not all salts are safe to eat — some are industrial or toxic compounds. The ones listed above are among the edible and physiologically relevant varieties. A few examples of common but inedible salts are:

•       MgSO₄ (Epsom Salt) — used in baths for muscle relief

•       Road Salt – While road salt is mostly sodium or potassium chloride it often contains dirt and other contaminants that make it not safe to eat.

To keep it simple language, an electrolyte is an edible salt that has been dissolved in water.

Key Electrolytes and Their Roles

Sodium

Sodium is the primary electrolyte in your body's extracellular fluid, and it plays a central role in regulating fluid balance and blood pressure. It also helps transmit nerve signals and supports muscle contractions.

That said, sodium is one electrolyte where overconsumption is a real concern — particularly in the American diet, which tends to be high in processed and packaged foods. The Dietary Guidelines for Americans recommend limiting sodium intake to less than 2,300 mg per day for most adults.

Athlete Note: Endurance athletes and those who sweat heavily may need more sodium than the standard recommendation, as significant amounts are lost through sweat during prolonged exercise. Sports dietitians often tailor sodium intake based on training intensity and individual sweat rate.

Potassium

Potassium works hand-in-hand with sodium to regulate fluid balance and supports healthy blood pressure. It's critical for proper muscle function, including the heart, and helps nerve signals travel throughout the body. Good dietary sources include bananas, sweet potatoes, leafy greens, and avocados.

Magnesium

Magnesium plays a key role in energy production, muscle and nerve function, blood sugar regulation, and protein synthesis. Magnesium also helps the body properly use calcium and potassium. Many people don't get enough magnesium from diet alone, making it a commonly depleted electrolyte.

Calcium

Best known for building strong bones and teeth, calcium also plays a role in muscle contractions, nerve signaling, and managing the heart’s rhythm. While most people think of calcium in the context of dairy products, it's also found in leafy greens, almonds, and fortified foods.

Chloride

Chloride is the negatively charged counterpart in many common edible salts. It is essential for maintaining fluid balance and proper blood pressure. It also plays a role in digestion as a component of stomach acid (hydrochloric acid).

It's worth clarifying: chloride (Cl⁻) is not the same as chlorine (Cl₂). Chlorine is a highly reactive toxic gas used as a disinfectant; chloride is a harmless, essential ion that your body uses every day. The small amount of chloride found in drinking water poses no health risk.

Phosphate

Phosphate works closely with calcium to build and maintain bones and teeth. It also plays an important role in energy metabolism and is a building block to the nucleotides that make up DNA. It's a key component of ATP (adenosine triphosphate); the molecule your cells use to store and transfer energy. Phosphate is found in most protein-rich foods, including meat, dairy, nuts, and legumes.

Bicarbonate

Bicarbonate acts as a buffer in the blood, helping to maintain a stable pH level. Your body constantly produces acids as a byproduct of metabolism, and bicarbonate neutralizes these acids to keep your blood from becoming too acidic. The lungs and kidneys work together to regulate bicarbonate levels.

The Supporting Role of Vitamins

Vitamins also play an important, if indirect, role in hydration and overall cellular health. Vitamins fall into two broad categories based on how the body stores and processes them:

Water-Soluble Vitamins

These include vitamin C and all eight B vitamins. Because they dissolve in water, they are not stored in the body for long periods — excess amounts are excreted through urine. This means you need a consistent daily intake. The upside is that toxicity from overconsumption is rare; the downside is that they must be regularly replenished through diet.

Fat-Soluble Vitamins

Vitamins A, D, E, and K dissolve in fat rather than water and can be stored in the body's fatty tissues and liver. This means they don't need to be consumed as frequently, but it also means that excess accumulation is possible, making very large doses of these vitamins potentially harmful.

While a deep dive into every vitamin and its role in hydration would fill an entire separate article, it's worth knowing that vitamins support the enzymatic processes that keep your cells functioning optimally.

Not All Drinks Are Created Equal: The Beverage Hydration Index

You might assume that any liquid you drink hydrates you equally, but that's not quite true. Researchers have developed what's known as the Beverage Hydration Index (BHI), which measures how well different drinks hydrate the body relative to plain water.

The BHI is influenced by a number of factors, including the electrolyte concentration, carbohydrates, and protein content of a beverage. Drinks with certain electrolytes, particularly sodium, have been shown to retain more fluid in the body and produce more effective rehydration than plain water.

The Sodium Sweet Spot

Research suggests that the optimal sodium concentration for rehydration beverages sits somewhere in the range of 40–75 millimoles per liter (mmol/L). At this level, sodium helps the body absorb and retain water more effectively than plain water can on its own, making it particularly valuable after exercise or illness when significant fluid has been lost.

This is the science behind why sports and electrolyte drinks can outperform plain water in certain recovery scenarios. It also explains why the classic advice to sip broth or electrolyte solutions when sick isn't just folk wisdom, it's grounded in solid physiology.

What About Restock?

Restock is formulated with approximately 40 mmol/L of sodium and around 20 mmol/L of potassium, placing its sodium content at the lower end of that optimal rehydration range. This makes it a practical option for everyday hydration support, particularly for active individuals or those recovering from mild fluid loss.

Additionally, Restock contains 4g/L protein which in conjunction with the electrolytes increases fluid retention even further.

The takeaway: for general hydration, water is excellent. For active recovery or rehydration after significant fluid loss, a beverage with electrolytes in the optimal range can be meaningfully more effective.

The Bottom Line

Hydration is far more than a daily water quota. It's a dynamic balance involving the water you consume, the nutrients that help your body use that water, and the many forces that drive fluid out of your body each day.

Understanding the basics — from why electrolytes matter, to what dehydration actually feels like, to which beverages are most effective for rehydration — puts you in a much stronger position to take care of yourself. Your body is roughly two-thirds water, staying hydrated is one of the simplest, most impactful things you can do for your health.

For more specific information on calculating what your body needs visit here:

https://www.nal.usda.gov/human-nutrition-and-food-safety/dri-calculator

https://ods.od.nih.gov/HealthInformation/nutrientrecommendations.aspx

Stay hydrated. Stay healthy.

Sources & References

GENERAL HYDRATION

National Institutes of Health — News in Health. "Hydrating for Health: Why Drinking Water Is So Important." NIH News in Health, May 2023. newsinhealth.nih.gov/2023/05/hydrating-health

NHS Inform (Scotland). "Hydration." NHS Inform. nhsinform.scot/campaigns/hydration/

ELECTROLYTES

Cleveland Clinic. "Electrolytes: Types, Purpose & Normal Levels." Cleveland Clinic Health Library. my.clevelandclinic.org/health/diagnostics/21790-electrolytes

National Cancer Institute. "Definition: Electrolyte." NCI Dictionary of Cancer Terms. U.S. Department of Health and Human Services. cancer.gov/publications/dictionaries/cancer-terms/def/electrolyte

National Institutes of Health — Office of Dietary Supplements. "Potassium: Health Professional Fact Sheet." NIH ODS. ods.od.nih.gov/factsheets/Potassium-HealthProfessional/

National Academies of Sciences, Engineering, and Medicine. "Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate." The National Academies Press, 2005. Available via NCBI Bookshelf: ncbi.nlm.nih.gov/books/NBK234935/

SODIUM & ATHLETIC PERFORMANCE

Veniamakis, E., Kaplanis, G., Voulgaris, P., & Nikolaidis, P. T. (2022). "Effects of Sodium Intake on Health and Performance in Endurance and Ultra-Endurance Sports." International Journal of Environmental Research and Public Health, 19(6), 3651. doi.org/10.3390/ijerph19063651 | Full text: pmc.ncbi.nlm.nih.gov/articles/PMC8955583/  — Peer-reviewed systematic review

BEVERAGE HYDRATION INDEX

Millard-Stafford, M., Snow, T. K., Jones, M. L., & Suh, H. (2021). "The Beverage Hydration Index: Influence of Electrolytes, Carbohydrate and Protein." Nutrients, 13(9), 2933. Georgia Institute of Technology, Exercise Physiology Laboratory. doi.org/10.3390/nu13092933  — Peer-reviewed study

DIETARY REFERENCE INTAKES & TOOLS

National Institutes of Health — Office of Dietary Supplements. "Nutrient Recommendations and Databases." NIH ODS. ods.od.nih.gov/HealthInformation/nutrientrecommendations.aspx

USDA National Agricultural Library. "Dietary Reference Intakes (DRI) Calculator for Healthcare Professionals." USDA NAL. nal.usda.gov/human-nutrition-and-food-safety/dri-calculator