IntroductionMaintain Body Fluids BalanceCredit:
Maintaining electrolyte, fluid and acid-base balance is one of the most important functions that the body is tasked. This dynamic mechanism is manifested in simple ways, like times where you feel like voiding every few minutes or times where you don’t urinate for hours at a time.
In order to function properly, the cell does not only depend on the continuous supply of the needed nutrients and the removal of metabolic waste but the cell also depends on the chemical and physical homeostasis of the surrounding fluids. 
Body Water Content
 Total Body Water RequiredCredit:
For a healthy young adult, about half of your body mass is probably water. Contrary to popular belief, there is no definite number that represents the amount of water found in our body. Total body water varies according the age, sex, body mass and the amount of body fat.  
Infants, having low bone mass and low body fat, are about 73% water which explains their dewy skin. As a person ages, the body water declines and by the time we reach the bracket of old age, we are composed of only 45% water in relation to our body mass. As stated earlier, a healthy man is about 60% water and a healthy young woman is about 50% water. What this explains is that females do have more body fat and has lesser skeletal muscles compared to that of men. Containing only 20% water, the adipose tissue is the least hydrated of all the body tissues. The skeletal muscle is one of the most hydrated, containing up to 75% water.
Fluid CompartmentsExtracellular and Intracellular Fluid Compartments BalanceCredit:
Two fluid compartments exist in our body, the intracellular fluid compartment or ICF and the extracellular fluid compartment or ECF. Almost two-thirds of water can be found within the ICF and the remaining one-third in the ECF. As we react to our environment, the cell also reacts to their environment, which is represented by the ECF. Two subcompartments compose the ECF, namely the plasma and the interstitial fluid. The plasma is the fluid portion of the blood and the interstitial fluid is the fluid which can be found in the microscopic spaces in between cells. 
Composition of Body Fluids
 Vital Importance of Body FluidsCredit:
Water, being the universal solvent can dissolve a wide array of solutes. Solutes in the body may be broadly classified into electrolytes and nonelectrolytes. Covalent bonds that exist in nonelectrolytes prevent it from creating electrically charges species when dissolved. What are included in the nonelectrolytes classification are mostly organic molecules like creatinine, lipids and glucose. 
On the other hand, electrolytes dissociate into ions when they are dissolved in water. Ions are electrically charged particles hence they have the ability to conduct electrical current, giving rise to the name electrolyte. Electrolyte, fluid and acid-base balance maintenanceCredit:
Water moves according to osmotic gradient, that is from an area of lesser osmolality to an area that has greater osmolality. In this instance, electrolytes have the greatest ability to cause fluid shifts. This great osmotic power the electrolytes possess is attributed to the fact that when they are dissolved, they dissociate into at least two ions.