To answer Dan87, we use 10% because that's what we always have used. Not a good reason, I know, which is why I googled this after reading your question. I found one post that states the heat transfer characteristics of components is different, like Scott said. Then I dug further and found a statement in "Textbook of Blood Banking and Transfusion Medicine" that said water is acceptable because it is less dense than the blood components and would, therefore, fluctuate faster than the blood components and allow action to be taken before said components would actually be affected. SO, I think we will stick with 10% since mostly what we have is packed red cells.