The term comes from the days of sail, because wind would blow from the
rear of the ship to the front. The bathroom would be located at the
front, "Head", of the ship to carry the foul smell of excrement away
from the crew.
On such old ships the “out house” was placed at the bow of the ship. These necessary rooms were placed in that forward area where the ship slanted inward to form the bow, which meant the toilet was above the ocean and not actually above the ship. Therefore, when nature called and you needed to use one of these facilities, you went forward to the bow or the “head“ of the vessel. Thus, the outhouse/toilet came to be called the "head".
On such old ships the “out house” was placed at the bow of the ship. These necessary rooms were placed in that forward area where the ship slanted inward to form the bow, which meant the toilet was above the ocean and not actually above the ship. Therefore, when nature called and you needed to use one of these facilities, you went forward to the bow or the “head“ of the vessel. Thus, the outhouse/toilet came to be called the "head".
