n restroom. The derivation comes from a long time ago. As derivations often do, now I think about it. What a lot of nonsense there is in here. Anyway, back then people used to shout “gardez l’eau” (the French equivalent of “look out for the water”) and throw their human waste out of the window onto gutters in the street. Of course, it wasn’t water at all, but perhaps we were all a bit too posh to shout “gardez le merde.” Another almost definitely spurious etymology is that in large mansions the toilet was always numbered room one-hundred to save any embarrassing confusions.