Sharecropper, I am sure that one drop is enough and your experience proves that.
Probably intentional overkill (as a safety factor), but for record I ran across this the other day:
https://www.epa.gov/ground-water-and-drinking-water/emergency-disinfection-drinking-water
What's funny is the article says something like bleach is "either 6% or 8%" (meaning the hypochlorite in solution).
I got a bottle of old common everyday Clorox:
- The label says "7.5%"
That's a hoot, right?!
Guess they should have added "or somewhere in between".