Waterfall soup is unlocked after completing the commission Logistics Disaster.
Once thats done you'll have access to array of options but more soups are unlocked after reaching certain Inter-knot level.
By level 20 and 30 you'll have alot of options and select the soups that aid your team.
Such as Pumpkin And Mushroom Soup Boost Physical Damage by 15 and 30% respectively.
Similar options are avaliable for Fire, Ice. and Ether etc. They just boost the affinity your characters are associated with.
Full list of all soups and their functions can be found here
Eat Ramen and benefit from temporary buffs at Waterfall Soup in Zenless Zone Zero (ZZZ). See all Ramen at Waterfall Soup, their buffs, cost, level requirement, and location here!