spelio has added a photo to the pool:
It will be DIFFICULT!
en.wiktiohttps://en.wiktionary.org/wiki/on_the_wagonnary….
Etymology
Originally on the water wagon or on the water cart, referring to carts used to hose down dusty roads:[1][2][3] see the 1901 quotation below. The suggestion is that a person who is “on the wagon” is drinking water rather than alcoholic beverages.
The term may have been used by the early 20th-century…
Source : https://www.flickr.com/photos/spelio/54400016995/in/pool-17918700@N00
