People seem to disagree quite a bit here. For my own routine the most cautious route is sticking to the thirty milliliter size of that water, though I have no idea how hard it might be to find in the UK. Another careful habit is tossing the vial a month after the first time it gets opened. I keep mine chilled and try not to go past that window. Even so plenty of folks stretch it further whenever the liquid stays clear and shows no sign of anything wrong. Since it is simple to replace where I live I just get a fresh one once the month is up. Some others who stay extra tidy report using theirs for two or three months without trouble. I forget the exact name but if you look through older threads there is supposedly a gadget that lets the vial stay usable longer.
As a beginner I'm trying to figure out if a 30ml bottle of BAC water, when I only reconstitute once a month, has to be discarded after a month because the syringe has gone into it. I know the usual guideline is about four weeks. Or can the same bottle be entered repeatedly? Mainly wondering whether the larger size is worth getting instead of 10ml or smaller.