 As a result, the colloidal or oncotic pressure of the higher level of protein in the plasma tends to draw water back into the blood vessels from the tissue.Starling's equation states that the rate of leakage of fluid is determined by the difference between the two forces and also by the permeability of the vessel wall to water, which determines the rate of flow for a given force imbalance.Most water leakage occurs in capillaries or post capillary venules, which have a semi-permeable membrane wall that allows water to pass more freely than protein.