Green’s Dictionary of Slang

sober-water n.

[the pun reflects its use as a partial cure for hangovers]

soda water.

[Ire]Roscommon Jrnl 26 Sept. 3/3: We happened to drop in for a glass of ‘sober water’.
[UK]Blackburn Standard 7 Oct. 1/4: The bottle contained nothing but ‘sober water’.
[UK]R.S. Surtees Handley Cross (1854) 305: ‘Have ye any swipes?’ ‘Sober-water and Seltzer-water,’ replied the boy.
Leicester Mercury 28 Feb. 2/1: Drink then to the days of old, / Be it wine or sober water.
Reynolds’s Newspaper (London) 9 Feb. 4/3: It is well for those who do not stint themselves the after-dinner pint of port, to recommend oatmeal and sober water.
[UK]‘Cuthbert Bede’ Little Mr. Bouncer 12: He’s not had no sober-water this morning, and I’m not aware as he were pleasant last night.
[UK]Farmer & Henley Sl. and Its Analogues.
Sporting Times (London) 6 Aug. 2/1: ‘I do not hold with diluted soda water (formally known as ‘sober water’) as the best of all morning beverages. A ‘peg’ certainly picks you up.
[UK]Birmingham Dly Gaz. 5 Jan. 4/7: ‘There is no better remedy for drunkenness than soda water.’ Hint for mineral manufacturers — re-name it ‘sober water’.