Not to be too much of a contrarian, but I'll wager giardia and crypto cysts will survive just fine in a bottle of vinegar, given they thrive in our acidic guts. Vinegar's acetic acid, and not very concentrated at that.

Regardless, as you rightly note a drop or even seven in a liter of water won't kill anything and will just make it taste like pickle juice. And if it's "hard" water, it will be instantly neutralized.

Back to our regularly scheduled programming.

Cheers,