Explanation:

- "Of the first water" is an idiom used to describe something that is of the highest quality or purity. The term originated from the gemstone industry, where diamonds were graded by their clarity and luster, with the clearest and most brilliant being described as "of the first water."

- Option 1: "Of ancient origin" suggests something very old or historical. This does not relate to the idiom's meaning.

- Option 2: "Of favorable opinion" implies a positive viewpoint. However, the idiom is more about inherent quality than opinion.

- Option 3: "Of no significance" implies something is unimportant, which is opposite to what the idiom means.

- Option 4: "Of the best quality" correctly captures the idiom's essence as it refers to superior quality or excellence.