«وَرُؤْيَتَهُ رِيًّا»
I considered the sight of him a quenching of thirst.
Ruʾyah is seeing; riyy is satisfaction of thirst. The closeness of the sounds makes a vivid comparison: seeing a beloved companion refreshes the heart as water refreshes a thirsty person.
The image is figurative. It communicates delight in the meeting, not an episode of literal drinking.