This is a nautical metaphor referring to the part of a ship's side near the waterline that is sometimes above the water and sometimes submerged; damage to the ship at this level is particularly dangerous. The phrase is first recorded in its literal sense at the time of the Spanish Armada ( 1588 ): ‘One of the shot was betweene the winde and the water, whereof they thought she would haue sonke’. By the mid 17th century, it was also being used of people.