What is the main ingredient used to flavor mango cactus water?

The correct choice identifies Mango Monin as the main ingredient used to flavor mango cactus water. Mango Monin is a concentrated syrup specifically designed to provide a robust mango flavor, which is central to the drink's profile. In the preparation of drinks like mango cactus water, the addition of this syrup enhances the overall taste, making it vibrant and appealing.

While other options like tequila and Espolon may provide alcoholic elements for cocktails, they are not components associated directly with the flavoring of mango cactus water itself. Soda water serves primarily as a mixer, contributing to the drink's texture but not its signature taste. Therefore, Mango Monin stands out as the key ingredient responsible for imparting the distinct mango flavor that characterizes this refreshing beverage.