The reason why Brits call toilets “loos” is one of the unsolved mysteries of etymology, however this is not for lack of trying! The word has been traced to rise into common usage around the 1920s, and plenty of theories exist surrounding the loo origins.
Here are four of the main theories:
Theory 1: Loo may be short for Waterloo, a common brand of cast iron toilet cisterns.
One theory is that in the 1900s Waterloo iron cisterns were a common component of British outhouse toilets. This idea is almost wholly derived from James Joyce’s referral to the Waterloo toilet in his 1922 text, Ulysses.
Some etymologists suggest that the word loo may have been coined by Joyce, made in reference to a joke about the battle of Waterloo.
Theory 2: Loo from Gardez l’eau
A colourful theory that sadly seems to have little evidence behind it is that in the days of the chamber pot, before proper plumbing systems existed, French people would chuck their chamber pot contents out of windows accompanied by the considerate shout to passers by on the street of: “gardez l’eau!” meaning “watch out for the water!”. The theory goes that “gardez l’eau” became mispronounced by Brits and corrupted to gardyloo, and eventually loo. The expression gardyloo seems to have been in circulation in some parts of Britain.
However, considering that the word loo was first documented many years after plumbing arose, and long after the phrases “gardez l’eau” and gardyloo were used, it seems unlikely that this was the origin of our modern word, loo.
Theory 3: Loo from a Ship’s Looward side
A ship’s leeward side is the opposite side to the windward side, where if you spat or took a leak off the side, your creations would successfully leap off the leeward side and into the sea as opposed to leaping back at you. The theory is that people relieved themselves from the leeward side so that it eventually came to be synonymous with the toilet side of the ship. Leeward was sometimes pronounced looward, which was shortened to loo.
This theory seems slightly dubious as most ships had a toilet at a place called the “ship’s head” at the bow of the ship, so why would they also use the leeward side?
Theory 4: Loo from lieux d’aisances or le lieu
The French phrase, lieux d’aisances translates to: place of easement; a euphemism for toilet. Another possible euphemism was calling it “le lieu”, the place. These phrases may have been picked up in France by British soldiers in World War I. The phrase may have been shortened to “lieux” and pronounced “loo”.
The date of this theory fits with the origin of the phrase around the early 1900s but there is little evidence in current existence to support this theory.
My theory is that it originated from bourdaloue, a urinary receptacle used particularly by ladies in times past.