More than half of the body weight corresponds to the presence of water, which is distributed across various spaces or compartments, including: the intracellular space and the extracellular space, the latter subdivided into the interstitial space and the intravascular space. For the body to function normally, it must prevent the fluid levels in these spaces from varying too much, as a disturbance in the fluid of one of these compartments can lead to what is known as an electrolyte imbalance. The control of fluid levels is closely related to electrolytes.