Bawls Guarana started as the brainchild of a then 20 year-old college graduate named Hoby Buppert, who was looking for an alternative to coffee in 1997. As part of a class project, he came up with a carbonated and non-alcoholic beverage made with guarana, a highly caffeinated berry native to the Amazonian rainforest. Named for the caffeinated "bounce" it gives you, which contains a natural form of caffeine nearly three times stronger than that found in traditional sodas.
Looking for a place to settle, Hoby Buppert chooses Texas, a quiet place, conducive to the growth of Guarana. The company markets its drinks only in Texas forever, never looking to emigrate because of the market leader, the Nuka-Cola Corporation. But before the Great War, Bawls Guarana concluded a lucrative contract with Vault-Tec, which wanted to build the Secret Vault in Texas. They sponsored the construction and only its product was allowed in the vault, at the expense of Nuka-Cola, non-existent in this region.
Despite advertising in Carbon, you can find Bawls bottles only in the Secret Vault, especially in the Bawls vending machine that contains 9 bottles (and 4 more if you destroy the machine). Each bottle will heal you 1/4 of your Hit Points until 2/5 with the skill First Aid at maximum level.
The in-game explanation to why there are only Bawls Guarana in Texas is that Nuka-Cola or someone else has never competed with Bawls Guarana in this region, and Bawls Guarana has never extended its business somewhere else. This makes it the only drink in the game, and replaced Nuka-Cola.