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Our body is mainly composed of water, which is excreted by the kidneys, lungs, and skin. Delivering it in appropriate quantities is key to ensuring the proper functioning of many body reactions. Water is indispensable for digestion, nutrient transport, removal of metabolic products, and maintaining body temperature at the right level. There are numerous mechanisms that help maintain proper water balance, but they can be disrupted, for example, by inadequate nutrition. Providing an adequate amount of minerals such as potassium and sodium is crucial here. Negative effects of excessive fluid intake rarely occur in healthy individuals, but the problem can arise in cases of one-time consumption of large amounts of fluid exceeding the maximum amount of water that the kidneys can excrete (600–1200 ml/hour). Too little consumed fluid can also lead to water retention. However, it is worth noting that a properly functioning body effectively excretes excess water and maintains a proper water balance.

Water management in the body is heavily dependent on electrolyte concentrations, such as sodium and potassium. They play a crucial role in maintaining the osmotic balance of the body in extracellular fluids by regulating the volume of water and protecting against dehydration. If the supply of electrolytes, such as sodium and potassium, is not sufficient, the composition of the extracellular fluid changes. Excessive consumption of fluids containing small amounts of electrolytes can lead to disturbances in the water-electrolyte balance, which can result in swelling and cell damage. This can lead to symptoms such as weakness, vomiting, nausea, loss of appetite, low blood pressure, and even convulsions or coma. Consuming liquids with an excessive amount of electrolytes, such as seawater, can also lead to negative effects, such as dehydration. This is caused by the flow of water from the circulatory system to the digestive system to balance the osmotic equilibrium. Therefore, it is extremely important to provide mineral components, such as sodium, in the correct amount. A deficiency in these mineral components is as dangerous as an excess. Special attention should be paid to moderate sodium intake, as there is currently too much of it in many food products. Products such as processed meats, smoked fish, yellow cheese, salted nuts, sticks, and ready-to-eat meals are particularly rich in sodium chloride. According to the World Health Organization (WHO), the daily intake of salt (NaCl) should not exceed 5 grams, which is equivalent to one flat teaspoon.

Preserving a constant fluid intake is key to maintaining adequate water balance in the body. It is vital to maintain equilibrium between ingested and excreted fluids. The body's fluid necessities vary and depend on numerous factors, such as ambient temperature, physical activity, or dietary composition. The World Health Organization recommends consuming at least 30 ml of water per kg of body weight daily. Nutritional recommendations are based on the adequate intake (AI) level, which determines the needs of most healthy and well-nourished individuals in a particular group. Currently, 2700 ml of water is recommended for women and 3700 ml for men.

A critical component of the water-electrolyte economy is vasopressin, often referred to as the antidiuretic hormone. When fluid intake is inadequate, the secretion of vasopressin increases, leading to water retention in the kidneys. The reabsorption of sodium increases while the excretion of potassium is enhanced, resulting in a decrease in urine volume and water excretion from the body. This leads to the retention of excessive water, known as hypervolemia, which causes edema and swelling. Hypervolemia can also occur in individuals with the syndrome of inappropriate antidiuretic hormone secretion (SIADH), where the pituitary gland secretes excessive amounts of the hormone, leading to water retention. Problems with water retention can also arise during the menstrual cycle, particularly in the luteal phase, when the aldosterone levels in urine and serum significantly increase. A decrease in the progesterone levels during this phase can directly contribute to an increase in aldosterone production, independent of the renin-angiotensin system. Aldosterone increases the reabsorption of sodium, leading to water retention in the body and a decrease in the potassium levels in the body fluids.

Swelling can also arise as an outcome of prolonged sitting periods, such as during work or travel. In such cases, blood and lymph flow more slowly through the network of blood vessels, which can impact the displacement of fluids into the tissues. The mentioned symptoms can also occur during heatwaves - the blood vessels dilate due to the high temperatures, facilitating the transmigration of water into the intercellular space. Moreover, these same symptoms can also be the result of excessive alcohol consumption.