Is a naturalistic language without count nouns possible, thus having only mass nouns? This would mean having many words for things with water: a sea, an ocean, a bottle of water, a puddle, etc.
What about compounding to get these words?
As a matter of fact, Mandarin Chinese can be considered to be such a language - it treats every noun as a mass noun. Every noun requires a "measure word" for counting, like "bottle" in "four bottles of water" or "sheet" in "ten sheets of paper". Chinese has a considerable list of these (https://en.wikipedia.org/wiki/List_of_Chinese_classifiers) but there's no particular reason that a language with only mass nouns would need to have so many classifiers.
Yes. A language can treat all nouns as mass nouns and require classifiers when counting objects.