Theoretically, (and on the Discworld theories of this nature tend to work, even if they are not actually right, owing to narrative causality), the bottle contains water from the cauldrons of Nac Mac Feegle keldas since before history.

This is called the theory of narrative causality and it means that a story, once started, takes a shape.

The only character who persists in constantly breaking the fourth wall by referencing, amongst other things, narrative causality, the gangster stereotype, and the freeform flow of the game itself.

However, these references may be just observations about the nature of discworld reality, since narrative causality is a fundamental law of the discworld universe.

This is rather similar to the Discworld concept of narrative causality.

A gingerbread house appeared in The Light Fantastic, whose owner had been shoved into her own oven, however this was a different witch (Goodie Whitlow) who met the same end due to narrative causality.

However, fairy godmothering is probably another aspect of witchcraft, relying heavily on narrative causality.

Due to the Disc's narrative causality such a person is almost always a highly-trained martial artist.

This is known as the law of narrative causality.

They play a far greater role in police procedure than narrative causality would like to admit.