I actually don't see any problem with using the sterile water alone. The reconstitution instructions are conservative to say the least. One vial shouldn't last more than a week anyway (due to 18 IUs or less being in a vial for most all brands), and one week refridgerated is no problem. I have BW, so I use that, but I wouldn't worry either way. The main thing is to be sterile and stay away from heat......those are the main contributors to degradation.