Tôi dùng một lượng nhỏ nước.

Here dùng means to use.

So:

• Tôi dùng... = I use...

It is very close in meaning to sử dụng, but there is a style difference:

• dùng = common, everyday, natural
• sử dụng = more formal, more written, a bit more official

So you could also say:

• Tôi sử dụng một lượng nhỏ nước.

That is correct, but it sounds more formal than the version with dùng.

Also, dùng can mean slightly different things depending on context, such as use, take, or even consume, but use is the best match here.

Một literally means one, but very often it also works like a/an in English.

So in this sentence:

• một lượng nhỏ nước = a small amount of water

You do not need to understand it as a strict numerical one every time. It often just introduces a singular countable unit or measure phrase.

Compare:

• một người = one person / a person
• một cái bàn = one table / a table
• một lượng nhỏ nước = a small amount of water

So yes, it literally comes from one, but in many sentences it functions much like English a.

Lượng means amount, quantity, or volume depending on context.

In this sentence, it helps express an amount of something that is not normally counted item by item.

So:

• lượng = amount / quantity
• một lượng nhỏ nước = a small amount of water

It is not a typical classifier like:

• cái for objects
• con for animals

Instead, it is better thought of as a measure noun or quantity noun.

English does something similar:

• a glass of water
• a bottle of milk
• an amount of water

Vietnamese also uses measure words and quantity nouns to talk about things like liquids, mass, or abstract amounts.

Nhỏ means small, and here it describes lượng, not nước.

So the structure is:

• một lượng nhỏ nước
• literally: one amount small water
• natural English: a small amount of water

This is because Vietnamese adjectives usually come after the noun they describe.

So:

• lượng nhỏ = small amount
• nhà lớn = big house
• xe mới = new car

In this phrase, nhỏ does not mean the water itself is small. It means the amount is small.

Vietnamese often does not need a separate word for English of in measure expressions.

So English says:

• a small amount of water

But Vietnamese can simply say:

• một lượng nhỏ nước

This is very normal in Vietnamese. The relationship is understood from the word order.

You see the same pattern in many common phrases:

• một cốc nước = a glass of water
• một chai sữa = a bottle of milk
• một ít đường = a little sugar

So the missing of is not actually missing from a Vietnamese point of view. Vietnamese just builds this kind of phrase differently.

Yes, absolutely — and in everyday speech, that is often more natural.

Compare:

• một lượng nhỏ nước = a small amount of water
• một ít nước = a little water / some water

Both are correct, but they feel slightly different:

• một lượng nhỏ nước sounds more explicit, a bit more formal, or more careful
• một ít nước sounds simpler and more conversational

In many situations, Vietnamese speakers would naturally say:

• Tôi dùng ít nước.
• Tôi dùng một ít nước.

Those often sound more everyday than Tôi dùng một lượng nhỏ nước.

It is grammatical and understandable, but it can sound a little more formal or deliberate than what people usually say in casual conversation.

More natural everyday alternatives might be:

• Tôi dùng ít nước. = I use little water.
• Tôi chỉ dùng một ít nước. = I only use a little water.

The original sentence is still fine, especially if you want to match the English idea of a small amount of water more closely, or if the context is slightly more formal, such as discussion about water usage.

So a good summary is:

• correct: yes
• natural: yes, but somewhat more formal or explicit
• most conversational: usually ít nước or một ít nước

Because nước here is not being counted as separate individual objects. It is treated like an uncountable substance, similar to water in English.

For uncountable things in Vietnamese, you often use a measure word or quantity word instead of a basic classifier.

That is exactly what lượng is doing here.

So instead of counting nước directly, Vietnamese counts the amount:

• một lượng nhỏ nước = a small amount of water

This is similar to English. You do not usually say one water when you mean the substance. You say:

• a little water
• a glass of water
• a bottle of water
• an amount of water

Vietnamese works in a similar way.

Sometimes yes, if the subject is clear from context.

Vietnamese often drops subjects when they are already understood. So in the right situation, someone might simply say:

• Dùng một lượng nhỏ nước thôi.
• Chỉ dùng ít nước.

However, when giving a full standalone sentence, especially for learners, including tôi is normal and helpful:

• Tôi dùng một lượng nhỏ nước.

So:

• with tôi = complete, clear, neutral
• without tôi = possible in context, but less explicit

Because Vietnamese words often have multiple meanings, and context tells you which one is intended.

Nước can mean:

• water
• country / nation
• sometimes other related meanings in certain expressions

In this sentence, the phrase một lượng nhỏ nước strongly points to the substance water, because a small amount of country does not make sense.

Also, the verb dùng fits naturally with water in the sense of using or consuming it.

So context makes the meaning clear.

They are very close, but not exactly identical in tone.

• Tôi dùng ít nước = I use little water / I don’t use much water
• Tôi dùng một lượng nhỏ nước = I use a small amount of water

The difference is mostly one of style:

• ít nước is shorter, more natural in speech, and more everyday
• một lượng nhỏ nước is more explicit and slightly more formal

So if you are just speaking naturally, Tôi dùng ít nước is often the better choice. If you want a phrasing closer to the English structure a small amount of water, then Tôi dùng một lượng nhỏ nước works well.