The document discusses the composition of body fluids and fluid loss. The total body water is divided into two compartments: intracellular fluid (ICF) and extracellular fluid (ECF). ICF makes up 30-40% of body weight and includes fluid inside cells, while ECF makes up 20% and includes interstitial fluid and plasma. Fluid loss in neonates includes insensible water loss of 15-30 ml/kg due to their high surface area to body mass ratio and thin skin. Other fluid losses include renal output, stool water, growth, and water from oxidation. An equilibrium is normally maintained between the ICF and ECF compartments.