“Perhaps no other word in English has undergone more transformations in its lifetime than toilet.
Originally, in about 1540, it was a diminutive form of toile, a word still used to describe a form of linen.
Then it became a cloth for use on dressing tables. Then it became the items on the dressing table (whence toiletries).
Then it became the dressing table itself,
then the act of dressing,
then the act of receiving visitors while dressing,
then the dressing room itself,
then any kind of private room near a bedroom,
then a room used lavatorially,
and finally the lavatory itself.
Which explains why toilet water in English can describe something you would gladly daub on your face or, simultaneously and more basically, water in the toilet.”
From “At Home”, Anchor Books 2010, by Bill Bryson, pp 417/418