I opened a 30 mL bacteriostatic water vial on June 9 and wrote the date on the cap. This week I pulled it out and the rubber stopper felt slightly tacky, plus there was a faint ring on the shelf under it. The liquid looked clear and I didn't see floaters.
I wiped the outside and set it aside, but now I'm unsure whether that's normal rubber residue or a sign the seal/contents are compromised. My usual check is open date plus a quick look, and I keep it out of light; that's not giving me much confidence here.
For people who've had this happen: what concrete signs made you decide a vial was done?
Do you log stopper feel or just date? If anyone has a solid source on storage or contamination signs, I'd rather read that than guess from social clips.