There is national coffee day, national donut day, national Taco day. Why isn't there a national ice water day? Tough to beat a big glass of ice water on a hot day.
I believe most of those "national XYZ days" come about thru trade organizations successfully lobbying Congress; the "day" amounts to free advertising for the product.
Which means that the ice water lobby is falling down on the job! Ice water sales must be lagging badly. When was the last time you bought a glass of ice water??
Probably because it's practically free so no one can make money out of encouraging people to do more of the thing. However I bet there could be a national fridge/freezer day...