Comparisons vs Parallelism (Sentence Correction)

[LazyNK]

Hello (Edited the two choices below by adding "Amount of"),
I have a doubt regarding comparisons with regards to parallelism. It is clear that the compared objects should be parallel in various aspects, and comparison should also make sense. While solving some of the sentence correction problems, I land up in situations where two answers are split between comparisons of the following type (just an example here) .

Choice 1 : "Amount of" water in glass A is more than glass B
Choice 2 : "Amount of" water in glass A is more than that in glass B

Both the splits are considered grammatically OK , but I always find myself spending valuable few tens of seconds deciding whether to eliminate choice-1 - because "water in glass A" can be more than "water in glass B" , but not more than "glass B" obviously.
Can you please explain when we can assume the words which are not present in a sentence ( In the above example, words "that in" are not present in Choice 1 but I believe are assumed to be present).
Thanks a lot,
NK

But I think I have come across answer choices where "choice-1" was part of the correct answer. I'd recheck and provide that particular question, along with its source. Thanks for your answer.

[tim]

these are NOT both grammatically correct. Choice 1 is wrong because it compares water to a glass. Choice 2 compares water to "that", which in this case refers to water. However, Choice 2 is also wrong because it is incorrect to say that water is more than something. You should instead say that the amount of water in glass A is more than that in glass B..