7. HUMAN EXCRETION RELATIVE WITH H2O the cells. Both the spaces between cells (intercellular spaces) and the spaces inside cells (intracellular spaces) are filled with water. Water lubricates joints and acts as shock absorbers inside the eyes and spinal cord. Amniotic fluid, which is largely water, protects the fetus from bumps and knocks. Water also helps the body maintain a constant temperature by acting as a thermostat. When a person is too hot, whether from being in a hot environment or from intense physical activity, the body sweats. When sweat evaporates, it lowers the body temperature and restores homeostasis .