Nước này nóng.

In Vietnamese, demonstratives such as này usually come after the noun, not before it.

So:

• nước này = this water
• nhà này = this house
• người này = this person

This is one of the first word-order differences English speakers notice.

Vietnamese often does not use a separate word for is before adjectives.

So:

• Nước này nóng. literally follows the pattern this water hot
• but in natural English, that means This water is hot

The adjective nóng can act as the predicate by itself.

Normally, no.

The word là is usually used to connect one noun to another, like A is B in an identity/equation sense:

• Anh ấy là giáo viên. = He is a teacher

But with adjectives like nóng, Vietnamese normally does not use là:

• Nước này nóng. = correct
• Nước này là nóng. = unnatural / usually incorrect

No. Nước is a very common word with several meanings, including:

• water
• liquid / drink
• country / nation

Context tells you which meaning is intended. In Nước này nóng, if the meaning shown to you is about temperature, then nước is being understood as water or liquid.

Here, yes: it means hot in temperature.

In other contexts, nóng can also mean things like:

• physically hot
• emotionally heated
• urgent / intense

But it is not the normal word for spicy. For spicy food, Vietnamese usually uses cay.

So:

• nước nóng = hot water
• món này cay = this dish is spicy

Because nước is a mass noun here, and Vietnamese does not always require a classifier with mass nouns.

So nước này is perfectly natural for this water.

You would use a classifier or measure word if you wanted to specify a container or unit, for example:

• ly nước này = this glass of water
• chai nước này = this bottle of water

But for just this water, no classifier is needed.

This is a very useful distinction:

• Nước này nóng. = This water is hot.
• nước nóng này = this hot water

In the first sentence, nóng is the main predicate of the sentence.

In the second phrase, nóng is part of the noun phrase, describing nước.

So English speakers can think of it like this:

• noun + này + adjective → often a full sentence
• noun + adjective + này → often a noun phrase

The biggest thing to pay attention to is the tones.

• nước has the sắc tone and ends in -c, so it is short and clipped
• này has the huyền tone, which is lower and falling
• nóng also has the sắc tone

So the tones are important:

• nước = sharp/rising, clipped
• này = low falling
• nóng = rising

Even if your vowels are not perfect yet, getting the tones roughly right will help a lot.

Yes. Those change the meaning from this to that.

For example:

• Nước này nóng. = This water is hot.
• Nước đó nóng. = That water is hot.
• Nước kia nóng. = That water over there is hot.

Very roughly:

• này = this
• đó = that
• kia = that over there

Yes. Nước này nóng. is a normal, complete Vietnamese sentence.

It has:

• a subject: nước này = this water
• a predicate: nóng = hot

Vietnamese often allows very short, clean sentences like this, especially in everyday speech.