Translation:It is water.
@Chaitanyad972223, か is often and in majority of the cases as a question (asking a question) article, (as far I'm aware and understand). So I think if the phrase was: それは水 (This is the Kanji for water - みず mizu) ですか. Then essentially it would read as a question - is it water.
TL/DR: Use を with direct objects and が with subjects. Replace the particle with は if you want to mark the noun as a topic.
First of all, you need to understand the noun is a subject, an object or a complement. In this case です literally means "exists as" so by the intranstive nature of the verb, it can only have a subject or a complement.
それ should be the subject of the verb exist, so you need a subject marker が to represent the relationship. Here you see は instead of が because the topic marker は supersede が so that it sets それ as a topic of the sentence.
If the noun is a direct object, then the particle を is used. Again, the object can be selected as a topic so the topic marker は can replace the を if it is needed.
Same treatment of は is used for complement nouns, but note that not all particles associated with the complements can be replaced with は, e.g. に、へ、と、で. In those cases, the は is appended to the particle instead.
それは水です - それ as a subject, so the は replaces the original が.
それは好きですか. それ as a complement （original sentence is それが好きです）
それは使います. それ as a direct object （original sentence is それを使います）
それには乗りません. それ as a complement （それに乗ります）
Hmm, I don't know if I can explain this very well, but 水 sort of does have an indicator, です.
As Keith mentioned, です behaves as an intransitive verb, in that it doesn't take a direct object. If you were to point to a part of the sentence which you could call "the object" though, it would be 水. です does the job of connecting it to the topic, in this case それ.
Adding to Keith's post, それ is the pronoun for an object, namely "it" or "that" in English. In order to say it's "there", you need the pronoun for a location, namely そこ in Japanese, to be present somewhere in the sentence.
Note also that you've changed the subject around when you go from "That is water" to "The water is there."
In the former, "that", or some unspecified thing, is being equated to "water". In the latter, "the water" is being specified as "existing there".
I was confused much the same way not even four months ago, until I looked through my brother's college textbook. Here's what I've learned: Japanese actually has four--count 'em, 4--demonstrative pronouns (well okay, they're technically 3 demonstratives and 1 interrogative, but most of the lessons that I came across taught them all together and the structure for them all is too similar so we'll go with four). They are "kore", "sore", "are", and "dore".
"kore" refers to anything that is close to the speaker in distance, especially anything that might be in the speaker's hand for instance, like "this thing near me".
"sore" is for anything that is closer to the listener than it is to the speaker, like "that thing near you".
"are" is for anything that is off in the distance away from both speaker and listener, like "that thing over there".
and "dore" is a ambiguous placeholder usually used in questions to ask "which one?"
You are also going to run into the "kono/sono/ano/dono" set soon. These "~no" words are just like the "~re" words except that they are adjectives rather than pronouns, and so must be followed by a noun. And there are even more Ko/So/A/Do sets where that came from...
I already explained ko/so/a/do words elsewhere in this discussion, so its worth finding.
As for the particles you've listed: wo/を is the (direct) object marker; it marks the noun that the verb is happining to. it's essentially the opposite of the subject marker ga/が, which marks the thing that is doing the verb.
Wa/は is the topic marker. I'm still learning when and where exactly to use this particle myself, but from what I understand myself, は is generally used once at the beginning of each entire paragraph or conversation to establish what the paragraph or conversation is about (with a few exceptions as always). If I'm right, then Duolingo's method teaching sentence-by-sentence is actually a pretty terrible way to convey the topic marker's purpose.
Finally to/と is usually a grouping marker. It has several uses and translations, but chances are you can easily transliterate it to English as "and" or "with".
Great answer! Just to clarify a couple of things:
- は can be, and often is, used multiple times in the course of a conversation/paragraph, even multiple times in the same sentence. Generally, to begin with, it's a good approximation to think of は as a particle that overrides another particle like が or を, simultaneously taking over its role and emphasizing the thing it's attached to.
- と is introduced in this course in one of the Intro levels, in sentences like 田中といいます. In this situation, its role is the "quotation particle" and it basically wraps quote marks around the noun/clause/sentence before it. If you fill out the implications of the example sentence, you get something along the lines of [私は][人が]田中といいます, which sort of awkwardly translates to "[About me,] [people] say "Tanaka"."
Why does 水 not need a particle?
Probably the same answer to "Why does 'water' not need a preposition in the sentence 'this is water'?"
In which cases are there "floating" sentence parts?
You mean some phrases that can move around in a sentence? Then probably the same as English.. "Water, this is." is not quite possible except in some conversation, so as "水です、それは".
Is this a question about English? It depends on the subject of the being verb. I can give you a list of conjugations:
I am , you are , he/she/it is , we are , you all are , they are
As you can see, if the subject is first-person singular (you know, "I"), then "are" changes to "am", and if third-person singular (pronouns like "he" "she" or "it"), then "are" changes to "is".
And in this sentence, "are" changes to "is" because water is referenced as an "it".
Never? Even if someone held up a bottle of clear liquid and asked you "what is this?"
Or what if someone poured some clear liquid in a glass, drank some and said "man this vodka is so weak..."? You could point to it and say "that is water. We don't leave vodka out for patients in a paediatric clinic..."
Any situation you could say it in English would generally also work in Japanese; use your imagination.
Besides, I think the intention of this (and any) exercise is not to memorize this exact sentence, but rather to introduce the concept of それ vs これ and あれ, the basic sentence structure of "That is X", and the vocabulary/kanji for "water" which is a very useful word to know in general (not just for pointing to it).