There is “water” in the human brain. The so-called “water” in the human brain is called cerebrospinal fluid (CSF). Cerebrospinal fluid (CSF) is usually found in the human brain. The composition of CSF is relatively sparse, with more than 99% of the fluid being water, and some proteins, sugars, and inorganic salts are also present. Cerebrospinal fluid is secreted in the brain every day and then passes through the various ventricles before eventually entering the subarachnoid space and flowing back into the bloodstream, where it is continuously absorbed. The continuous production and absorption of cerebrospinal fluid can supply nutrients to brain cells, take away some metabolic products from brain tissues, regulate the acid-base balance of the central nervous system, and cushion the pressure on the brain and spinal cord, which protects and supports the brain and spinal cord.