Nước mắm ở trên bàn.

In Vietnamese, location sentences usually do not use là.

So:

• Nước mắm ở trên bàn. = The fish sauce is on the table.

Here, ở handles the idea of being located somewhere.

Use là for things like:

• Đây là nước mắm. = This is fish sauce.
• Anh ấy là giáo viên. = He is a teacher.

But for location, là would sound wrong here.
So Nước mắm là trên bàn is not natural Vietnamese.

They have different jobs:

• ở = at, in, located at
• trên = on, above

Together, ở trên means something like is located on.

So:

• ở bàn would mean something like at the table
• trên bàn means on the table
• ở trên bàn makes the location relationship extra clear: is on the table

A very literal breakdown is:

• Nước mắm = fish sauce
• ở = located at
• trên bàn = on the table

Yes, sometimes, but it can sound different.

Nước mắm ở trên bàn is a clear full sentence:

• The fish sauce is on the table.

Nước mắm trên bàn can be understood in conversation, but it may also sound like a noun phrase:

• the fish sauce on the table

So if you want a clear, complete statement for a beginner, ở is safer and more standard.

Nước mắm is a fixed expression meaning fish sauce.

Its parts are:

• nước = water, liquid
• mắm = fermented fish/seafood product

But you should learn nước mắm as one vocabulary item, not as a fully predictable word-for-word phrase like water sauce.

It is the normal Vietnamese term for fish sauce.

Vietnamese usually does not use articles like a, an, and the the way English does.

So bàn can mean:

• a table
• the table

The exact meaning depends on context.

In your sentence, if the meaning shown is on the table, that comes from context, not from a separate word meaning the.

Classifiers are common in Vietnamese, but they are not required in every sentence.

You can say:

• trên bàn = on the table
• trên cái bàn = on the table / on that table

Adding cái can make the noun feel more concrete or more spoken, but it is often omitted when the noun is already clear.

Also, nước mắm is a mass noun here, so it does not need a classifier in this sentence.

If you were talking about a bottle, you might say:

• chai nước mắm = bottle of fish sauce

It can mean table or desk, depending on context.

Examples:

• bàn ăn = dining table
• bàn làm việc = desk / work table

In Nước mắm ở trên bàn, the most natural English translation is usually table, because fish sauce is something you expect on a table.

Yes, it can still be okay if the context makes it obvious.

In everyday speech, Vietnamese often names the substance or item generally, even when the actual object is a container.

So Nước mắm ở trên bàn may be understood as:

• The fish sauce is on the table and people may imagine a bottle.

But if you want to be more specific, say:

• Chai nước mắm ở trên bàn. = The bottle of fish sauce is on the table.

The pattern is:

• noun + ở + location

So:

• Nước mắm = subject/topic
• ở trên bàn = location

This is a very common Vietnamese pattern.

You can compare:

• Sách ở trên ghế. = The book is on the chair.
• Mèo ở dưới bàn. = The cat is under the table.

Yes, but the meaning or focus changes a little.

For example:

• Ở trên bàn có nước mắm. = There is fish sauce on the table.

This pattern uses có and introduces what exists in that place.

Compare:

• Nước mắm ở trên bàn. = The fish sauce is on the table.
• Ở trên bàn có nước mắm. = There is fish sauce on the table.

The first talks about where the fish sauce is.
The second talks about what is on the table.

A rough pronunciation guide is:

• nước ≈ nướk
• mắm ≈ mam with a short ending
• ở ≈ a short vowel somewhat like uh with a dipping tone
• trên ≈ chane / train without the final English sound exactly
• bàn ≈ bahn with a falling tone

A few useful tone notes:

• nước: rising tone
• mắm: rising tone
• ở: dipping tone
• trên: level tone
• bàn: falling tone

Pronunciation varies by region, so the exact sound may differ between Northern, Central, and Southern Vietnamese.