Made me smile... or would have, if I wasn't a German Very Serious Person. ;)

I don't think "drill" is such a good translation though. Höhlen comes from "Höhle", meaning "cave". Maybe a better translation:

Steady water hollows the stone.

And you got to admit that the "German assumption of hardness" is actually pretty accurate when it comes to stones! (Except those in Brazil, presumably.)