Phrase origin

HI there, can anyone tell me the origin & meaning of the phrase "still waters run deep"? I know that it means that there can be turmoil beneath the surface etc, but I am wanting a more difinitive definition & I thought the origin might help me.

Cheers - Deb

Dear Deborah,
As far as I know, it is used to describe someone who is quiet, but actually has deep thoughts and can quietly do meaningful things (at least that's the meaning of the idiom in Hebrew).

Ruth