* Someone who enjoys drinking water from rivers: This is technically possible, but not recommended due to potential contamination.
* Someone who enjoys being near rivers: This could be a person who loves spending time fishing, kayaking, or just admiring the scenery by the water.
* A playful metaphor: Perhaps "river drinker" is a term used to describe someone who is constantly thirsty for new experiences, or who loves to travel and explore.
* A made-up term: It's possible the term is entirely fictional and has no specific meaning.
If you can give me more context, I can help you figure out what it means. For example, where did you hear this phrase? What was the situation?