so literally a waters glass. comparing to romanic languages where for example in spanish you would say un vaso DE agua, polish eliminates the prepostition with the genitive case right?
Right. It's good to always imagine this "of" (even if it's not literally there in the English sentence sometimes) which causes Genitive.
exactly speaking I do not drink a glass but drink water, but szklanka takes biernik case?
So in the sentence, "On potrzebuje szklanki wody" the ending of szklank is different because potrzebuje puts it in genitive, right? Thanks for the help!