Shows my age, but a lot of pop coolers in stores were that way when I was growing up. Just a big metal bathtub full of water, with refrigeration equipment undnerneath to keep the water cold. This probably evolved from earlier versions using ice.
“Malt does more than Milton can / To justify God’s ways to man”
-A. E. Housman (1859–1936). A Shropshire Lad , 1896.