Определение и Значение "(as) dull as ditchwater"

What is the origin of the idiom "dull as dishwater" and when to use it?

The origin of the idiom "dull as dishwater" is not definitively known, but it emerged in the 19th century. It draws a comparison between dishwater, which is typically bland and lacking in interest or excitement, and something that is uninteresting, boring, or lacking in liveliness. The phrase is used to suggest a lack of stimulation, creativity, or engaging qualities, emphasizing a dullness that fails to capture attention or evoke enthusiasm.