Tôi xin một chút nước.

In this sentence, xin means to ask for / request.

So Tôi xin một chút nước is literally something like:

• Tôi = I
• xin = ask for / request
• một chút = a little
• nước = water

A very important nuance: xin often sounds more polite than just a bare command. It can carry the idea of “may I have...” or “I’d like to ask for...” depending on context.

However, in everyday speech, many people would more naturally say:

• Cho tôi xin một chút nước.

That sounds more complete and very common in real life.

Yes. Tôi is just one way to say I in Vietnamese, and it is fairly neutral and polite.

Vietnamese pronouns depend a lot on:

• your age compared with the listener
• your relationship with the listener
• formality
• region and situation

So instead of tôi, you might hear:

• em if you are younger than the person you are speaking to
• con when speaking to parents or older family members
• cháu when speaking to grandparents or older adults
• mình in some casual situations

For example:

• Cho em xin một chút nước. = May I have a little water?
  (said by someone younger to someone older)

So the sentence is grammatically fine with tôi, but in real life the pronoun may change.

Vietnamese word order here is straightforward:

• subject + verb + object

So:

• Tôi = subject
• xin = verb
• một chút nước = object

That is why Tôi xin một chút nước is natural.

English learners sometimes expect the quantity expression to work differently, but in Vietnamese một chút comes before the noun it modifies:

• một chút nước = a little water

So the structure is:

• xin + một chút nước
• ask for + a little water

Yes, một chút means a little / a small amount / a bit.

In this sentence, it softens the request and shows you only want a small amount of water.

Common similar expressions are:

• một chút = a little / a bit
• một ít = a little / some
• một tí = a tiny bit, very conversational
• chút by itself = a little

Examples:

• một chút nước = a little water
• một ít tiền = a little money / some money
• đợi một chút = wait a moment

So yes, it works a lot like English a little, but it is also very common as a softener in requests.

Both can mean a little water, and both are natural.

A rough difference is:

• một chút often feels a bit more like a little bit
• một ít often feels a bit more like a small amount / some

But in many everyday situations, they overlap a lot.

For this sentence:

• Tôi xin một chút nước.
• Tôi xin một ít nước.

Both are understandable and acceptable.

In casual speech, people often prefer whatever sounds more natural to them personally or regionally. You do not need to worry too much about a strict rule here.

Because Vietnamese does not need an of here.

English says:

• a little water
• a bit of water

Vietnamese simply puts the quantity expression before the noun:

• một chút nước

So you can think of it as a built-in pattern:

• một chút + noun
• một ít + noun

Examples:

• một chút thời gian = a little time
• một ít gạo = a little rice / some rice

You do not insert a separate word for of.

No. Nước has several meanings, so context matters.

Common meanings include:

• water
• liquid/drink in some contexts
• country/nation

Examples:

• uống nước = drink water / have a drink
• nước cam = orange juice
• đất nước = country, nation

In một chút nước, the meaning is clearly water because of the context.

If you want to be more specific, you could say:

• nước lọc = plain drinking water
• nước uống = drinking water
• nước lạnh = cold water

It is understandable and reasonably polite, but by itself it can sound a little bookish or slightly incomplete in some situations.

A more natural everyday version is often:

• Cho tôi xin một chút nước.

Why? Because cho adds the sense of give/let me have, which is very common in requests.

Other natural options:

• Cho tôi xin chút nước.
• Làm ơn cho tôi xin một chút nước. = Please give me a little water.
• Cho em xin ít nước ạ. = polite, with a different pronoun and sentence-final politeness particle

So your sentence is correct, but in conversation many speakers would choose a version with cho.

Cho literally means give, but in requests it often helps form a natural expression meaning:

• please give me...
• let me have...
• may I have...

So:

• Tôi xin một chút nước = I ask for a little water
• Cho tôi xin một chút nước = Please let me have a little water / Please give me a little water

This cho ... xin pattern is extremely common in spoken Vietnamese.

It is useful to learn these request patterns:

• Cho tôi xin...
• Cho em xin...
• Làm ơn cho tôi xin...

They are often more natural than using xin alone.

Yes, very often you can.

These are all possible:

• một chút nước
• chút nước
• một ít nước
• ít nước

In everyday conversation, people often drop một.

So:

• Cho tôi xin chút nước.

is very natural.

Using một can sound a bit more complete or careful, but leaving it out is common and normal.

A simple pronunciation guide:

• Tôi ≈ toy (with the Vietnamese ôi sound)
• xin ≈ somewhat like sin, but with a lighter Vietnamese x
• một ≈ roughly moht, with a short clipped ending
• chút ≈ roughly choot, with a rising tone
• nước ≈ roughly noo-uhk said as one syllable, with a heavy tone

The tones matter a lot:

• tôi — level-ish
• xin — level
• một — low/heavy tone
• chút — rising sharp tone
• nước — heavy/glottalized tone

If you ignore the tones, people may still guess your meaning from context, but correct tones make a big difference in being understood.

Yes. Vietnamese often does not match English word-for-word.

A sentence like Tôi xin một chút nước can function as a polite request, even without a separate word for can.

English often uses:

• Can I have... ?
• Could I have... ?
• May I have... ?

Vietnamese often expresses the same idea through:

• the verb xin
• polite particles
• context
• intonation

So the politeness and request meaning come from the whole expression, not from a direct equivalent of English can.

Possibly, but more likely they would say a slightly more natural spoken version, such as:

• Cho tôi xin chút nước.
• Cho tôi xin một ly nước. = Please give me a glass of water.
• Cho em xin ít nước ạ. = polite, depending on who is speaking

In real life, speakers often specify the container too:

• một ly nước = a glass of water
• một chai nước = a bottle of water
• một cốc nước = a cup/glass of water

So if you are in a restaurant, Cho tôi xin một ly nước may sound more natural than just asking for a little water, unless you really do mean only a small amount.