Hypovolemia is characterized by volume depletion or dehydration.
It is a loss of the extracellular salt. The loss is through the gastrointestinal tract ( hemorrhage, diarrhea, vomiting) or kidney ( diuresis). This leads to circulatory collapse /instability and an increase in the serum urea nitrogen to creatinine ratio as a results of contraction of the total intravascular pool of plasma.
It is a loss of intracellular water.Leads to cellular desiccation. Increase in serum solution and plasma osmolality.
However, volume depletion and hypovolemia do not depend on each other.Volume depletion occurs with / without hypovolemia so does hypovolemia.