Water and inorganic salts (electrolytes) are important components of the organism and of body fluids. Body fluid is the internal environment for cellular life activities, and its constant volume, osmotic pressure, pH and appropriate concentration of various ions play an important role in ensuring the normal metabolism of cells. For example, hypotonic dehydration is the simultaneous deficiency of water and sodium, but the deficiency of water is less than the loss of sodium. This condition is an imbalance in the metabolism of water and inorganic salts. Isotonic dehydration is also known as acute or mixed dehydration. Because water and sodium are lost in proportion to each other, serum sodium remains in the normal range and the osmolarity of the extracellular fluid can remain normal. However, isotonic dehydration can cause a rapid decrease in the amount of extracellular fluid (including circulating blood volume). Treatment actively addresses the causative cause. For extracellular fluid sodium deficiency more than water deficiency and blood volume deficiency in mild sodium deficiency, although serum sodium may not be significantly changed yet, the amount of sodium chloride in urine is often reduced, and salt-containing solution or hypertonic saline is used for intravenous infusion to correct the hypotonic state of body fluids and replenish blood volume. The intake of high fiber and fresh vegetables and fruits, balanced nutrition, including protein, sugar, fat, vitamins, trace elements and dietary fiber and other essential nutrients, meat and vegetables, diversified food varieties, giving full play to the complementary role of nutrients between foods, is also very helpful in the prevention of this disease.