Explain how the use of distilled water in place of this saline solution would be expected to upset the patient's homeostasis?

The saline solution used in hospital I.V.s is a solution with about the same water concentration as the human body. If distilled water were used instead, the imbalance of concentrations of salt between the water and the body would cause cells to react, and the process of osmosis to cause them to bloat up with water, potentially damaging them.