Saturday, May 6 marks National Beverage Day, yet another obscure entry on the calendar that seems to be only slightly more respectable than, say, National Weatherperson’s Day (February 5).

It’s typically beverage manufacturers that make the most of these occasions, and you’re likely to come across invitations on social media from carbonated or flavored drink makers to “celebrate” by buying lots of sugar water. That was more or less the motive in 1921, when one of the earliest recorded mentions of a National Beverage Day—then called Bottled Carbonated Beverage Day—can be spotted. An unnamed contributor to The Re-Ly-On Bottler, a trade magazine dedicated to educating beverage producers, urged regional bottlers to utilize as many radio and newspaper resources as they could to promote their carbonated community.

“Give the public a new slant on the subject of drinking,” read the fizzy propaganda. “Let them know that carbonated beverages properly made and bottled are held in the highest regard by pure food authorities.”

Assuring consumers that bottled soda was free from impurities was a high priority. Inconsistent and nonexistent government oversight had plagued the food industry at the turn of the century, with inaccurate labels and suspect ingredients. The U.S. government even set up a “poison squad” in 1902 to see how adulterants like borax would be tolerated in volunteers. With consumers becoming more educated about what they were putting on their tables and into their bodies, bottlers wanted to soothe worries over contamination. In organizing a day devoted to the cause, the American Bottlers of Carbonated Beverages could marshal their ad efforts to promote carbonation as a kind of homogenization process—and even something downright healthy.

“Carbonic Gas is an enemy of the bacteria which menace us in food and drink,” read a 1925 ad in the Hartford Courant. “This is the gas which puts the bubbles in bottled carbonated beverages. It is pure of itself and it promotes purity in the beverages of which it is a part ... The thoughtful housewife will always have a case … in her home.”

Soda, the ad insisted, “contains more energy-forming material than many foods.” A graph showing that 16 ounces of soda contained 157 calories proved the point: that was far more than cabbages or turnips.

An ad in The Monroe News-Star that same year was more direct. “In days gone by, consumers … were very skeptical, for the reason they believed soda water was injurious to health, thinking it was made out of harmful ingredients and in an unsanitary plant, and right they were.”

Thanks to more restrictive state sanitary laws, the ad continued, that was no longer a concern. Soda was “pure” and “wholesome.” The notice was posted by Grapico Bottling, which assured readers they could “drink freely” and still “need no doctor.”

It’s hard to pinpoint exactly when Bottled Carbonated Beverage Day permanently became the less specific National Beverage Day, as ads throughout the 1920s alternately referred to it as National Carbonated Beverage Day or simply Beverage Day, among others. But in 1925, bottlers decreed it an annual event to be held the first Wednesday of each May. As time went on, there became less of a need to reassure soda enthusiasts that bottlers had eliminated “every vestige of germs.” They also may have had increasing trouble propagating the notion of soda as “healthful.” We don’t think National Eat Your Vegetables Day ever had this problem.