Many, many years ago I had a display of water guns at a local gun show. It included the Daisy Demoulin set with the water dipper that I got from Arni Dunathan. The title of my display was "HIJKLMNO GUNS". Of course I had several questions, what is HIJKLMNO. Simply, it is the letters H to O. What is the formula for water - H2O.
I thought it was a unique approach. However I can not take credit for it as I saw it on a Bazooka Joe bubble gum comic.
Note, there is presently a water dipper on ebay.