Kad idem u grad, uvijek nosim vodu sa sobom.

Yes. In this sentence, kad introduces a time clause, so it means when:

• Kad idem u grad... = When I go to town / when I’m going into town...

Croatian kad is very common in everyday speech. You may also see kada, which means the same thing but can sound a bit more formal or careful.

So:

• kad = common, everyday
• kada = same meaning, slightly more formal

Ići is the infinitive, meaning to go.
Idem is the 1st person singular present tense form, meaning I go / I am going.

The verb ići is conjugated like this in the present:

• ja idem = I go
• ti ideš = you go
• on/ona/ono ide = he/she/it goes
• mi idemo = we go
• vi idete = you go
• oni/one/ona idu = they go

So in Kad idem u grad, the subject is I, so idem is the correct form.

Because Croatian often leaves out subject pronouns when they are already clear from the verb ending.

• idem already tells you the subject is I
• so ja is usually unnecessary

You could say:

• Kad ja idem u grad...

But that would usually add emphasis, like When I go to town... as opposed to someone else.

This is very normal in Croatian:

• Idem kući. = I’m going home.
• Nosim vodu. = I carry water / I’m carrying water.

Because u can take different cases depending on whether it shows movement toward a place or location in a place.

Here, idem u grad means I go into town / to town, so there is movement. That requires the accusative:

• u grad = into town, to town

Compare:

• u gradu = in town, in the city

So:

• Idem u grad. = I’m going to town.
• Ja sam u gradu. = I’m in town.

This is a very important Croatian pattern:

• u + accusative = motion toward
• u + locative = location in

Literally, grad means city or town, depending on context. In this sentence, ići u grad is a very common expression that often means something like:

• go into town
• go downtown
• go to the city center

So even if grad literally means city, the phrase can feel more idiomatic than that. It often refers to going to the main urban area, center, or shopping/social area.

Uvijek means always.

In this sentence:

• Kad idem u grad, uvijek nosim vodu sa sobom.
• When I go to town, I always carry water with me.

Its position is natural because it comes before the main verb nosim.

That is a very common placement:

• Uvijek pijem kavu. = I always drink coffee.
• Uvijek kasni. = He/She is always late.

Croatian word order is fairly flexible, but uvijek often appears near the verb it modifies.

Nositi can mean several related things in Croatian, including:

• to carry
• to wear
• sometimes more generally to bear / bring along

In this sentence, nosim vodu clearly means I carry water or I bring water with me.

Examples:

• Nosim torbu. = I’m carrying a bag.
• Nosim kaput. = I’m wearing a coat.

So the exact meaning depends on context.

Because voda is the direct object of nosim, and direct objects often go in the accusative case.

• nominative: voda = water
• accusative: vodu = water (as the object)

So:

• Voda je hladna. = The water is cold.
  Here voda is the subject, so nominative.
• Nosim vodu. = I carry water.
  Here vodu is the object, so accusative.

This is a very common feminine noun pattern:

• žena → ženu
• kava → kavu
• voda → vodu

Sa sobom means with oneself / with me / with you / with him/her, depending on the subject.

In this sentence:

• nosim vodu sa sobom = I carry water with me

The word sobom comes from the reflexive pronoun sebe. After the preposition sa (with), it appears in the correct case form:

• sa sobom = with oneself

Because the subject is I, English translates it as with me.

Examples:

• Nosim putovnicu sa sobom. = I carry my passport with me.
• Povedi djecu sa sobom. = Take the children with you.
• Uvijek ima knjigu sa sobom. = He/She always has a book with him/her.

Good question. Both can relate to English with me, but they are used differently.

• sa mnom = with me, together with me
• sa sobom = with oneself, on one’s person, along with oneself

In this sentence, nosim vodu sa sobom means the water is on me / with me / carried along by me. That is why sa sobom is the natural idiom.

Compare:

• Ana ide sa mnom u grad. = Ana is going to town with me.
  Here it means together with me.

• Nosim dokumente sa sobom. = I carry the documents with me.
  Here it means I have them on me / I bring them along.

So sa sobom is the idiomatic choice for carrying or having something on your person.

Croatian has both s and sa, and both can mean with.
Sa is often used for easier pronunciation, especially before certain consonant clusters or sounds.

In many cases:

• s tobom
• sa sobom

The form sa sobom is the normal standard expression.

So here, sa is used because that is the natural fixed form: sa sobom.

Sobom is in the instrumental case, because the preposition s/sa meaning with normally takes instrumental.

So:

• sa sobom = with oneself
• sa mnom = with me
• s prijateljem = with a friend

This is why the sentence has:

• vodu in accusative, because it is the direct object
• sobom in instrumental, because it follows sa

It mainly describes a habit or a repeated action.

• Kad idem u grad, uvijek nosim vodu sa sobom.
• When I go to town, I always carry water with me.

The clue is uvijek (always), which strongly suggests a habitual meaning.

In Croatian, the present tense often covers both:

• general habits
• repeated actions
• actions happening now

So idem and nosim are present tense forms, but the overall sentence is understood as a general habit.

Yes, Croatian word order is more flexible than English, though some versions sound more natural than others.

The original:

• Kad idem u grad, uvijek nosim vodu sa sobom.

Possible variations:

• Uvijek nosim vodu sa sobom kad idem u grad.
• Kad idem u grad, vodu uvijek nosim sa sobom.

These are still understandable, but the original is very natural and neutral.

Croatian word order often changes for:

• emphasis
• rhythm
• focus

English is stricter, while Croatian allows more movement as long as the grammar is clear.

It can feel like either one in English, depending on context.

Because the sentence includes uvijek (always), the full meaning is close to:

• Whenever I go to town, I always take water with me

But natural English would usually just say:

• When I go to town, I always carry water with me

So Croatian kad here works well for repeated situations, even where English might sometimes prefer whenever.

Yes, that is possible, but it changes the nuance.

• nosim vodu focuses on carrying / having water with me
• ponesem vodu focuses more on taking / bringing some water along

So:

• Uvijek nosim vodu sa sobom. = I always carry water with me.
• Uvijek ponesem vodu. = I always take some water with me.

Both can work, but nosim vodu sa sobom strongly highlights the idea of keeping it with you.

Yes, two very useful patterns:

• ići u grad = to go into town / go downtown
• nositi nešto sa sobom = to carry something with you / have something on you

These are common and worth learning as chunks, not just word by word.

So you can reuse them easily:

• Kad idem u grad, nosim kišobran sa sobom.
  When I go to town, I carry an umbrella with me.

• Uvijek nosi dokumente sa sobom.
  He/She always carries documents with him/her.