The origin of the phrase "still waters run deep" is not known for sure, though some seem to think it grew out of the watering hole culture of the US Appalachian area during the early years of the twentieth century.
It's a metaphor used for describing something that may not be exactly as it seems. An example of this is as follows:
- Cletus: Hey there, Bruce. You'll never guess what Old Uncle Jim got me for Christmas. He done knitted me a sweater, a red one, he knitted it his own self.
- Bruce: Do what now, Cletus? I never would'a guessed that he was the knittin' type.
- Cletus: Sure enough, he is. You know, still waters run deep.
- Bruce: Amen to that, cousin. I think we ought to go an' shoot the pansy.
- Cletus: You said it, Bruce. Drive the pickup 'round back to the shed, and I'll get the Remington.
Others believe it to be a relic of the first and second world wars. This makes sense, as it would perhaps be used to indicate the presence of enemy submarines or U-boats coasting a league or two beneath the surface of otherwise calm bodies of water.
StrawberryFrog informs me that the phrase's origin might be in Afrikaans: "I am reminded of an old Afrikaans proverb: 'Stille water, diepe grond, onder loop die duivel rond,' i.e. 'Still water, deep ground, 'neath the devil walks around.' what it means is that those Calvinists didn't trust introverts."
It was, perhaps, used to its greatest effect in the episode of Aqua Teen Hunger Force entitled "Balloonenstein."
In it, the Aqua Teens' neighbor Carl is standing in his back yard, admiring his newly decorated above-ground swimming pool. The exterior has been decked out in gold trim and neon light fixtures shaped like bolts of lightning. Running his hairy hand along its edge, he intones the following from his mental library of extremely memorable lines:
- Oh, sweet, sweet nectar. It's like my pool is tearin' ass around the back yard! But it's stayin' still. Still waters run deep.
Carl is voiced by Dave Willis, in a thick, dead-on New Jersey accent. "Balloonenstein" is episode #5, and it originally aired on December 21, 2001.
Still Waters Run Deep is also the title of a song by no less than nine different recording artists, including The BeeGees and Rick Wakeman.