I haven't tested it yet. I co tacted Steri Pen about warranty and what on it is water proof. No response on warranty and the top is not waterproof. Warranty is supposedly on Steri Pen website, but for this model it isn't. Also have a question about how do you get past the bad stuff on inside/outside rim of bottle/cup?
This review was written in the old system and had content requirements that are different than reviews written today.