According to Wikipedia, "The bidet appears to have been an invention of French furniture makers in the late 17th century, although no exact date or inventor is known. The earliest written reference to the bidet is in 1726 in Italy."
Several websites do however credit Christophe des Rosiers with installing one of the first bidets. The American bidet manufacturer Omigo, for example, says that "In 1710, the [French] royal family's furniture–maker, Christophe des Rosiers, installed the first bidet in the palace"; but it doesn't say that he invented it. It does say that "The history of the bidet began when a French craftsman invented a piece of furniture with a basin for water set into a stand with legs", but it still doesn't name the craftsman in question as des Rosiers or anyone else.
So ... as with so many 'inventions', it would appear that no one person invented the bidet – although Christophe des Rosiers probably did create at least one of the earliest examples.
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