That makes perfect sense.

At one point, many years ago, I read that earth’s water cycle is such that, at some point, you’ve drunk Napoleon’s urine. The author didn’t show their math, but let’s assume it’s true. We can take the same approach to holy water.

We might make the assumption that all water on earth has holy water mixed in with it, like cosmic background radiation. Now, obviously it doesn’t have sufficient holiness to be considered fully holy water - it doesn’t damage such creatures as vampires, possessed children, or Jews - but it’s necessarily present in at least trace amounts. And it would increase as a function of time.