Water 7 is the all blue ok.think of this when they are in water 7 the old man that sanji meets cooks with salt of laguna blue right but at the end he says the salt is from all water minerals in the world then when luffy helps the girl out finding her frien blue fin they find fish in one location the all blue is under water 7 when iceburg raises the citie of water 7 sanjis gonna find the all blue finally.
Then again is just a theory and has been proven wrong so I guess not.