first water

The term originated in the gemstone trade, where it was used to signify water-like clarity.

first water (uncountable)

1. The highest quality of gemstones, especially of diamonds and pearls.
   • 1854 August 9, Henry D[avid] Thoreau, “The Ponds”, in Walden; or, Life in the Woods, Boston, Mass.: Ticknor and Fields, →OCLC:

     Who knows in how many unremembered nations’ literatures this has been the Castalian Fountain? or what nymphs presided over it in the Golden Age? It is a gem of the first water which Concord wears in her coronet.

   • 1880, HB Cornwall, “Gems and Precious Stones”, in WM Patterson, editor, The Growing world; or, Progress of civilization, and the wonders of nature, science, literature and art, interspersed with a useful and entertaining collection of miscellany‎, page 20:

     To be the first water a diamond must be absolutely colorless, very lustrous, and perfectly free from flaws.

   • 1915, L[ucy] M[aud] Montgomery, Anne of the Island, New York, N.Y.: A[lbert] L[evi] Burt Company, →OCLC:

     “Here’s one I wrote. My heroine is disporting herself at a ball ‘glittering from head to foot with large diamonds of the first water.’

2. (by extension) The highest rank or quality or the greatest degree.

   He's a liar, swindler, and hypocrite—a scoundrel of the first water.

   • 1897, Mark Twain [pseudonym; Samuel Langhorne Clemens], “[Pudd’nhead Wilson] Chapter”, in The Tragedy of Pudd’nhead Wilson: And the Comedy Those Extraordinary Twins, Hartford, Conn.: American Publishing Company, →OCLC, page 135:

     Dave’s just an all-round genius—a genius of the first water, gentlemen; […]

   • 1897, Bram Stoker, chapter XX, in Dracula, New York, N.Y.: Modern Library, →OCLC:

     This was manifestly a prig of the first water, and there was no use arguing with him.

   • 1922, Robert C. Benchley, chapter XXII, in Love Conquers All, Henry Holt & Company, page 111:

     “A nice, juicy steak,” he is said to have called for, “French fries, apple pie and a cup of coffee.” It is probable that he really said “a coff of cuppee,” however, as he was a wag of the first water and loved a joke as well as the next king.

   • 1934 February, Cecil J. Allen, “British Locomotive Practice & Performance”, in Railway Magazine, pages 93–94:

     Presumably this was another case in which an engine had failed and had been replaced at short notice; certain it is that none but experts of the very first water could have coaxed such amazing work out of an engine of such comparatively small dimensions.

• of the first water

• first-degree (adj)

• first water on Wikipedia.Wikipedia