Bloody Hell and Holy Water?

Blood in Water

I long ago puzzled over this saying:

"Blood is thicker than water."

I knew it meant that your blood relatives were closer to you than all the rest of humanity, and thus deserved your loyalty, but why should "water" stand for everyone else?

I went into a deep thunk about it, and the solution eventually came to me: "baptism."

Baptism brought one into the family of God, such that people all the world over, potentially all of us, were relatives.

Relatives by water, of course, and thus not so thick, not so close as blood relatives, but relatives all the same . . .

(I'm not claiming, of course, that this is Christian doctrine . . .)