This is the 403rd most frequent Portuguese word.
mais
"Mais" means "more" or "most" in English.
Here, 'mais' is used for expressing proportional relationships in a correlative conjunction structure.
Quanto mais estudo, mais aprendo.
The more I study, the more I learn.
Here, 'mais' is used to request an additional amount of something, in this case, water.
Eu quero mais água.
I want more water.
In this sentence, 'mais' functions as a comparative, indicating a greater degree of a quality (interestingness).