First, times is a plural noun in your sentence. And two times indicates two of this same noun. You can't use an adverb in the blank below:
There is/are two _____ as much/many in this glass as in the other one.
This is verified by the Oxford English Dictionary:
- In plural Preceded by a number
a. Expressing comparison:
followed by an adjective or adverb in the comparative degree (e.g. ten times bigger, ten times more slowly, ten times less), or by as or (now rare) so with an adverb of quantity (e.g. ten times as (or so) many (as), ten times as (or so) much (as)).
Notice we can say either
two times as much ______ as
two times as many ______ as
depending upon whether the noun in the blank is a mass noun or count noun. We use much with mass nouns and many with count nouns.
It is precisely because water here is being used as a mass noun that we use is:
In this glass, there is two times as much water as in that glass.
Take away the comparison terms and you are left with
In this glass there is water.
Now if we are comparing a count noun, we can use are:
In this glass there are two times as many ice cubes as in that glass.
And this is an expanded version of
In this glass there are ice cubes.
So far, so good. But now comes a big caveat. Many native speakers will use there's in this case also, either because they are considering the ice cubes as a single set or because there's is a frozen form that is used by native speakers even if the following noun is plural.
In this glass there's two times as many ice cubes as in that glass.
Many native speakers will even use there's for the reduced sentence
In this glass there's ice cubes.
Some native speakers will find that clumsy, terrible sounding and downright ungrammatical. But the point remains that there's is used by native speakers to refer to more than one of something. See Can we use "there is" for plural nouns? (especially the accepted answer).
So, for the above reason, you can say either
There are two liters of water.
There's two liters of water.
But you probably should use are in writing and formal spoken English.