Het ijs op het water is dun.

Because both ijs and water are het-words in Dutch.

Dutch nouns usually take either de or het as their definite article:

• de for many common-gender nouns
• het for neuter nouns

So:

• het ijs
• het water

The two instances of het are not related to each other here. Each one is simply the article belonging to its own noun.

Because dun comes after the verb is and is being used as a predicate adjective.

In Dutch:

• attributive adjective (before a noun): usually -e
  
  • het dunne ijs
• predicative adjective (after zijn, worden, etc.): usually no -e
  
  • Het ijs is dun

So:

• het dunne ijs = the thin ice
• Het ijs is dun = the ice is thin

This is a very common pattern in Dutch.

Op het water is a prepositional phrase describing where the ice is.

It attaches naturally to het ijs:

• het ijs op het water = the ice on the water

So the structure is:

• Het ijs op het water = subject
• is = verb
• dun = adjective/complement

It does not mean that the water is thin. It means the ice that is on top of the water is thin.

Because ice in this context is understood as lying on the surface of the water, not being inside it.

• op het water = on the water / on the surface of the water
• in het water = in the water

If you said ijs in het water, that would suggest ice pieces floating or being inside the water.
But het ijs op het water refers to a layer of ice covering the water’s surface.

No. Here het is just the definite article, meaning the.

So:

• het water = the water

Dutch het can also be a pronoun in other sentences, but not here.

In this sentence, both uses of het are simply articles:

• het ijs
• het water

No, this is normal Dutch word order.

The sentence follows the basic pattern:

Subject + verb + complement

Here that is:

• Het ijs op het water = subject
• is = verb
• dun = complement/adjective

So it is very close to English word order:

• The ice on the water is thin

The only thing learners may notice is that the subject is a bit longer because it includes the phrase op het water.

Yes. That is a perfectly natural shorter sentence.

• Het ijs is dun = The ice is thin.
• Het ijs op het water is dun = The ice on the water is thin.

The longer version gives more context and specifies which ice you mean.
The shorter version is enough if the context is already clear.

It can mean both, depending on context.

• ijs = ice
• ijs = ice cream

In this sentence, op het water makes it clear that ijs means frozen water, not ice cream.

This is very normal in Dutch, and context usually removes any ambiguity.

IJs is pronounced roughly like English ice.

A few pronunciation notes:

• ij is a common Dutch vowel combination, often sounding somewhat like English eye
• the final s is just s

So ijs is close to ice, though the exact Dutch vowel may vary a little by region.

A natural pronunciation is roughly:

het eys op het WAA-ter is dun

A few points:

• het is often reduced in normal speech, almost like ut or h’t
• ijs sounds close to ice
• water in Dutch is usually WAA-ter, not like English waw-der
• dun has a short vowel, a bit like the vowel in English duh, but shorter and cleaner

The main stress usually falls on the important content words:

• IJS
• WAA-ter
• DUN

Yes, but it is not a full sentence by itself.

• het dunne ijs op het water = the thin ice on the water

That is a noun phrase, not a complete statement.

To make it a sentence, you need a verb:

• Het dunne ijs op het water is gevaarlijk.
• Het ijs op het water is dun.

This is a useful contrast:

• het dunne ijs = adjective before the noun → dunne
• het ijs is dun = adjective after the verb → dun

Because dun is an adjective, not a noun.

Articles like de and het go with nouns:

• het ijs
• het water

But dun describes the subject after the verb is, so it stands on its own as an adjective:

• Het ijs is dun

That is the same basic idea as in English:

• the ice → article + noun
• is thin → verb + adjective