Assuming that the era of the song is from blackpowder days, the powder consisted mainly of a nitrate and some "filler." The filler was usually a mix of sulphur and sugar - at least in the "home-brew" powder days.

Nitrates are very much soluble in water, so even slight amounts of water render the powder inert (but maybe tasty?).

As I recall, the third or fourth of the "General Rules of Action" for Rogers Rangers - well known in US scouting groups - is "Always keep your powder dry."

John