Everything you need to know about water

Water is a basic element of the human body, vital for organ function and thermoregulation. More substances dissolve in water than in any other solvent.

Water is a basic element of the human body, vital for organ function and thermoregulation. More substances dissolve in water than in any other solvent. Most of the chemical reactions that take place in our cells require water. Water is needed to transport nutrients and oxygen to all cells in the body. It helps convert food into energy and assimilate nutrients. Water keeps the body temperature stable and protects vital organs, is involved in maintaining the shape of cells and organs, and is important for healthy skin. Water helps the body to get rid of waste products: many toxins come out with sweat and urine, water (tears, saliva) washes out and dilutes caustic substances. Water also promotes breathing.

Water makes up about 2/3 of our body weight. The amount of water in the body depends on age, in infants it is 75%, in adolescents 65%, in adults 60% and in the elderly 55% of body weight.

The amount of water in the body is inversely proportional to the amount of adipose tissue, with severe obesity its amount drops even to 40% of body weight. Approximately 2/3 of all water in the body is found inside cells and 1/3 outside cells. Regulation of water balance is closely related to electrolyte balance. If there is too much water in the body, more liquid urine is excreted, and if the concentration of electrolytes in the body fluids becomes too high, the thirst center in the brain gets stimulated, which leads to a feeling of thirst, and the excretion of water by the kidneys decreases. Fluid loss occurs with urine and feces, and it also evaporates through the skin and respiratory tract. In a healthy adult, the daily amount of urine exceeds 600 ml and is normally 1-2.5 liters. 100-200 ml per day are usually excreted in the faeces, but this amount increases markedly with diarrhoea. A person loses on average 300-500 ml of water per day per m2 of body surface due to evaporation in a moderate climate. Losses with sweat are usually not great, but they increase to several liters a day in hot and humid environments or even in moderate conditions with hard physical work.

Water Demand

Most healthy people meet their daily water needs based on the feeling of thirst. There are no definitive recommendations for water intake for healthy people, because water requirements vary markedly from person to person and are influenced by physical activity and climatic conditions.

The need for water depends on a multitude of physiological and activity-related circumstances:

  • age,
  • nature of work and activities,
  • health status,
  • local climate,
  • increased sweating (hot weather, heavy physical work),
  • increased salt intake.

Thirst usually occurs when the body does not get enough water, loses a lot of fluid or receives too many mineral salts with food, especially table salt. The water requirement of an adult is 28-35 ml per kilogram of body weight (about 1 ml per 1 kcal of food energy). Virtually all foods contain more or less water.

In a normal diet, the basic amount of water comes with food (about 1-1.2 liters):

  • of fruits and vegetables,
  • soups,
  • teas,
  • coffee,
  • juices and other drinks.

In the course of metabolism, an additional 300-350 ml of water is produced. Thus, an adult who follows the dietary recommendations can drink an additional 2-3 glasses of water per day (according to the international standard, the volume of a glass is 220 ml).

You should always prefer drinking water without additives to quench your thirst. The need for water in infants and children is relatively higher, because the water content in their bodies is also higher. If children and adolescents, regardless of their age, are thirsty, they should always be given water, because the body is already signaling thirst through the desire to drink.

Caffeine flushes out water especially in those who do not drink it regularly (coffee, cola drinks, energy drinks). Alcohol (except for moderate amounts of beer and wine) also eliminates water from the body.

Moderate dehydration, which is the loss of 1-2% of body weight due to fluid loss, is accompanied by headache, a feeling of weakness, loss of appetite and dizziness. Dehydration of 3-5% of body weight lowers resilience and strength and leads to severe exhaustion. Dehydration of 15-25% of body weight is fatal. Acute poisoning is described when a large amount of fluid is ingested in a short time, exceeding the maximum rate of its excretion by the kidneys: 0.7-1 liters/hour.

Water content in products:

  • in vegetables averages 93% (e.g., 97% in cucumbers),
  • juices and milk 89%,
  • fruits 86%,
  • potatoes 79%
  • in meat 68%,
  • bread, cheese, butter, flour, nuts less than 50%.

What else is good to know about water:

  • Pure water and mineral water do not give energy, but in the presence of flavors or vitamins can contain a small amount of sugar and thus give energy. Read the package!
  • Prolonged and excessive drinking of water puts strain on the heart and kidneys.
  • When drinking mineral water, it is important to pay attention to its mineral content.
  • In case of sweating, slightly salty water is the ideal drink to replenish the salt reserves of the body.
  • Caffeine-containing coffee, tea and cola drinks, as well as alcoholic beverages increase the excretion of water from the body, speeding up kidney function and increasing sweating.