I could be mistaken but I believe that Serostim becomes much less stable once mixed with water of any kind. In fact the instructions (yeah, those!) say not to shoot the water directly at the wafer. At first I thought that this had to do with "foaming up" but now I understand that even this amount of physical force combined with the tugging of the water molecules on the Serostim hgh molecules could cause them to break up and become useless or decrease the effectiveness of the whole solution. Accordingly, I would also be careful not to drop it, once mixed, and handle it carefully. It is fairly stable and has a long shelf life if not mixed and kept out of the heat and sun. Remember full retail price for the stuff is something like $1500 per each kit of 7 vials of 6mg of Serostim plus 7 vials of 1 ml of sterile water (it also comes in other doses).
As for sterile water or bacteriostatic water, they supply sterile water. I understand they do this because the benzyl alcohol interacts with the serostim and damages it. A lot of people used to argue that they supplied it the way they did so you couldn't keep it mixed and had to use it up and increase sales. I think that is total BS. I believe they supply it the way they do because their information indicates that is the best way.
I talked to a rep from Serono Labs, makers of Serostim and he said they only make 9 pounds of the stuff per year at full production capacity. So I suspect they already have plenty of demand for what they produce and would have to find a way to increase the production before they had to worry about increasing sales.