Someone else confirmed, but yes, Apple Cider Vinegar.

I use it at home to kill stuff. When I butcher a chicken, I soak it in ACV afterwards, instead of bleach. When I get foot fungus, I soak my feet in it, better than anything at the drug store, and cheaper. I use distilled vinegar to clean out a fish tank. Bleach will kill the fish.

I have no doubt that ACV will kill all nasties in water. But I don't think 1 drop will work in a liter of water, probably need much more. Again, no test to look at. So, for the weight, ClO2.