Ne mogu progutati lijek bez vode.

Croatian often drops subject pronouns when they are not needed.

In ne mogu, the verb form mogu already tells you the subject is I:

• mogu = I can
• možeš = you can
• može = he/she/it can

So Ne mogu progutati lijek bez vode naturally means I can’t swallow the medicine without water.

You could add ja:

• Ja ne mogu progutati lijek bez vode.

But that usually adds emphasis, like:

• I can’t swallow it without water.

In Croatian, negation with most verbs is formed with ne + verb, written as two separate words.

So:

• mogu = I can
• ne mogu = I cannot / I can’t

That is the normal standard spelling.

Because moći (to be able to / can) is a modal verb, and modal verbs are followed by another verb in the infinitive.

So the structure is:

• ne mogu = I can’t
• progutati = to swallow

Together:

• Ne mogu progutati = I can’t swallow

This is similar to English can + verb:

• I can swallow
• I can’t swallow

This is about aspect, which is very important in Croatian.

• gutati = imperfective
  
  • swallowing in general, repeatedly, or as an ongoing action
• progutati = perfective
  
  • to swallow successfully, to get something down as a complete action

In this sentence, the speaker means a single completed act of swallowing the medicine, so progutati is the natural choice.

Compare:

• Ne mogu gutati tablete. = I can’t swallow tablets / I’m bad at swallowing tablets in general.
• Ne mogu progutati ovaj lijek. = I can’t swallow this medicine / I can’t get this medicine down.

Because lijek is the direct object of progutati, so it goes in the accusative case.

For a masculine inanimate noun like lijek, the accusative singular is the same as the nominative singular.

So:

• nominative: lijek
• accusative: lijek

That is why the form does not change here.

A useful comparison:

• masculine animate nouns usually do change in the accusative
• masculine inanimate nouns often do not

Vode is in the genitive case because it follows the preposition bez.

The preposition bez means without, and it requires the genitive.

So:

• voda = water
• bez vode = without water

This is a very common pattern in Croatian:

• bez šećera = without sugar
• bez pomoći = without help
• bez vode = without water

Here it is singular.

Why? Because:

• the basic noun is voda = water
• after bez, you need the genitive singular: vode

So:

• bez vode = without water

It is true that vode can also be a plural form in other contexts, but not here. In this sentence, the preposition bez clearly tells you that vode is genitive singular.

Croatian has no articles like English a/an and the.

So:

• lijek can mean a medicine, the medicine, medicine, depending on context
• voda can mean water, the water, depending on context

The listener understands from the situation what is meant.

That means English often has to choose:

• I can’t swallow the medicine without water
• I can’t swallow a pill without water

Croatian leaves that more open unless the context makes it specific.

Yes. Croatian word order is fairly flexible, because case endings show grammatical relationships.

The neutral, natural order here is:

• Ne mogu progutati lijek bez vode.

But other orders are possible for emphasis, for example:

• Lijek ne mogu progutati bez vode.
• Bez vode ne mogu progutati lijek.

These all mean roughly the same thing, but the focus changes:

• Lijek... emphasizes the medicine
• Bez vode... emphasizes the lack of water

So the original sentence is the most straightforward version.

You could, but it would not mean exactly the same thing.

• Ne mogu progutati lijek bez vode
  = I can’t swallow the medicine / I can’t get it down without water

• Ne mogu gutati lijek bez vode
  = I can’t swallow medicine without water / I’m unable to do that kind of action

The second version sounds more general or habitual, while the first sounds more like one specific swallowing event.

The cluster lj is a single Croatian sound, not a full English-style l plus y pronounced separately.

In lijek:

• li sounds roughly like lee
• je sounds roughly like ye
• k is a clear k

A rough English-style approximation is something like lyehk or lyek, but not exactly.

Two helpful pronunciation notes:

• j in Croatian is usually like English y in yes
• lj is a special palatal sound, somewhat like the lli in some pronunciations of million, though not identical

So lijek is approximately lyek.

Yes, moći (to be able to) is a somewhat irregular verb, and learners usually memorize its present-tense forms early.

Present tense:

• mogu = I can
• možeš = you can
• može = he/she/it can
• možemo = we can
• možete = you can
• mogu = they can

So in your sentence:

• ne mogu = I can’t

It is a very common verb, so it is worth learning well.