It depends on the size of the vial your peptide came in, if you need to dilute say 5mgs, you might want to add 5cc of Bac water to it, you can't get that into most little vials. You will lose more active compound with a more concentrated solution, plus its hard to draw up like 2 units in a 30 unit syringe. My preference is to reconstitute, transfer then dose from the new multidose vial. Alternatively, you can waste 20cc's of water from a 30cc bac water, then use that as your multidose vial. Depends if you care about cost of your Bac water....I don't YMMV