as the definition of "shui guo "in the Encyclopedia,水果是指多汁且美味的植物果实，不但含有丰富的营养?而且能够帮助消化。(shui guo shi zhi duo zhi qie mei wei de zhi wu guo shi,bu dan han you feng fu de ying yang,er qie neng gou bang zhu xiao hua).that is "shui guo"is part of a tree or bush(the fruit of plant),something juicy and tastes good .it also contains rich nutritions and is helpful with digesting. actually,really because of the bulk of the fruit are juicy your question is quite good! there isn't any Linguist has studied it as far as i know. hope it is helpfull

first,水果 in Chinese is one word and can't be separated second,果and国 are same in pronouncation and different in tunes,and of course different in meaning.国can be translated into "country"

果 means fruit, 水果 means fruit rich in water or juice and the others that are dry are called 干果. the both two are 果实. 果 can also mean a girl but it's a slang in some special fields

it's just a chinese vocabulary like fruit is an english vocabulary.

国 guo 2 果 guo 3 Their pronunciations are different and the characters are also different.