Why would using distilled water instead of saline solution in an IV upset a patients homeostaisis?

By using distilled water instead of a balanced solution of electrolytes such as saline or a lactated ringer, you will disrupt the osmotic balance of the red blood cells among other things. Most importantly, the red blood cells are isotonic with the surrounding blood plasma or serum, but by adding distilled water to this plasma, the plasma is now hypotonic to the RBC, so water will cross the membrane of the RBC and eventually cause the cell to rupture, or lyse. This will happen to other cells as well, with different effects. One you have red cell lysis, however, you get a whole host of other problems such as hemoglobinuria andmost likely pola, anemia and so on and so forth, all of which disrupts the overall homeostasis.