The Functions of Water in the Body - Daily Intake... Are We Truly Aware of How Much Water We Should Drink Daily?

Water plays a vital role in the essential processes of our body. It is present both inside cells and in the extracellular space, as well as within the vascular system. Maintaining water and electrolyte balance under various physiological conditions requires not only appropriate ion concentration but also the availability of energy substrates. The majority of water is located inside cells, while the extracellular compartment contains a slightly smaller amount. Water is essential for proper bodily function. Even a minor water deficit (2–3%) can lead to circulatory disturbances, such as increased blood viscosity and reduced vessel filling. The central nervous system exhibits symptoms like impaired concentration, headaches, fatigue, and loss of appetite. As dehydration progresses, it can result in altered consciousness, up to loss of consciousness. Mild dehydration is defined as a water deficit of up to 5%, moderate dehydration as up to 10%, and severe dehydration as up to 15%.

Water accounts for roughly 60-70% of an adult's body weight. Its quantity in the body varies depending on factors such as age, sex, and fat content. Children and adolescents exhibit a higher water proportion, whereas older individuals, women, and overweight persons have a lower water content due to a higher fat percentage. Notably, the water content in a newborn's body reaches 75%, whereas it decreases to 50% in older individuals. Water is present in all body tissues and fluids. It constitutes approximately 80% in blood, 73% in muscle, 25% in fat, and 10% in bones [3].

Water is an essential component of the human body, performing a wide range of vital functions. It forms the foundation of bodily structure, maintaining integrity and enabling metabolic processes. As a solvent, it facilitates the transport and absorption of essential substances. Water provides the environment where biochemical reactions crucial for survival occur. Additionally, it participates in digestion by aiding food formation, movement through the digestive tract, and enzyme activity. Water also distributes nutrients and metabolic byproducts throughout the body. It regulates body temperature, preventing overheating through evaporation, and sustains tissue elasticity while protecting the body's surface [2].

The human body cannot produce sufficient water to meet its needs, which is why we classify water as an essential nutrient. Individual water requirements depend on factors such as age, physiological state, physical activity level, presence of certain conditions (e.g., diabetes, kidney dysfunction), environmental factors like temperature and humidity, and dietary composition. It is calculated based on the amount of water needed to replace losses and dilute metabolic waste excreted by the kidneys. The minimal water intake required to meet these needs and prevent pathological changes is approximately 800–1000 cm3 per day. However, water consumption should not exceed the kidneys' excretory capacity. It is generally advised that adults consume 30 cm3 of water per kilogram of body weight. Some sources recommend 1 cm3 of water per 1 kcal of consumed food. Infants and elderly individuals, due to their reduced ability to concentrate urine, should consume 1.5 cm3 of water per 1 kcal of food. In practice, an adult woman in moderate temperatures and moderate physical activity should drink 2 liters of water daily, while an adult man should drink 2.5 liters. The water requirement for pregnant and lactating women is higher. Water is a vital nutrient that performs numerous essential functions in the body.