I don’t know of any testing, but it probably is. But then, so is everything else.
Perhaps someone could see about testing, that is if it hasn’t already been done. If people are worried about this, and the church decides to do something about it, then probably a bit of bleach would disinfect the water of most germs, although it might be sort of hard on the brass or bronze of the holy water container. Or is that brass or bronze? Is it gold plate? If so, then no worries.
Wash your hand when you get home, and carry some wipes or alcohol gels in your car. That should be more than enough.
If you have tiny tots, are taking care of somebody with a compromised immune system, or are taking care of an old person, then going the extra mile to take care of them is a good idea.
I’m not the last word on the subject, my post being based solely on conjecture. If anybody knows for sure, please feel free to chime in. I too am interested in hearing about any actual studies.