Learn Hardcore Croatian: On stalno nosi bocu vode sa sobom. - He constantly carries a bottle of water with him.

On stalno nosi bocu vode sa sobom. – He always carries a bottle of water with him. (neutral, maybe slight emphasis on he)
Stalno nosi bocu vode sa sobom. – (He) always carries a bottle of water with him. (most natural in context)

Croatian is a “pro‑drop” language: the verb ending -i in nosi already shows it’s he/she.
You keep On mainly:

to emphasize he (contrast: He does, others don’t)
at the start of a new topic or when it’s not clear who you’re talking about.

What tense and aspect is nosi, and why not something else like nositi or ponijeti?

Nosi is:

present tense
3rd person singular
of the verb nositi (to carry, to wear)
imperfective aspect (ongoing / repeated action)

You use nosi here because the sentence describes a habitual action – something he does regularly.

Compare:

On stalno nosi bocu vode sa sobom. – He always carries a bottle of water with him. (habit)
On će ponijeti bocu vode sa sobom. – He will bring a bottle of water with him. (one occasion, completed action; ponijeti is perfective)
Bare nositi is the infinitive, not a finite verb, so it can’t stand alone in this sentence.

Does nosi mean both “carries” and “wears”? How do I know which one is meant?

Yes, nositi can mean both to carry and to wear. The meaning comes from context.

On stalno nosi bocu vode sa sobom. – Here bocu vode (bottle of water) is an object you carry, not wear.
On stalno nosi kapu. – He always wears a cap.
On stalno nosi torbu. – Can be “He always carries a bag” or “He always wears a bag (on his shoulder)”, depending on the type of bag.

If it’s clothing or something on the body, nositi is usually “wear”.
If it’s an item in the hand, backpack, etc., it’s “carry”.

Why is it bocu and not boca in bocu vode?

Bocu is the accusative singular form of boca (bottle).

The pattern is:

nominative (dictionary form): boca – a bottle
accusative (direct object, “what does he carry?”): bocu – a bottle

So:

Boca je na stolu. – The bottle is on the table. (subject → nominative)
On nosi bocu. – He carries a bottle. (direct object → accusative)

In On stalno nosi bocu vode sa sobom., bocu is the direct object of nosi, so it must be in the accusative.

Why is it vode and not vodu after bocu?

Vode is the genitive singular of voda (water).

The structure boca + genitive is very common and means “a bottle of something”:

boca vode – a bottle of water
boca vina – a bottle of wine
boca mlijeka – a bottle of milk

So:

bocu vode = boca (accusative: bocu) + vode (genitive)
→ “a bottle of water” as a direct object.

If you said bocu vodu, that would be two accusatives together and incorrect in standard Croatian.

What case is sa sobom, and why do we use sa with that case?

In sa sobom, sobom is the instrumental singular of sebe (reflexive pronoun “oneself”).

The preposition s/sa (with) is followed by the instrumental case:

s prijateljem – with a friend
s tobom – with you
sa sobom – with oneself / with him- or herself

So the pattern is:

s/sa + instrumental

Sa sobom literally means “with himself / herself / oneself” in this context.

Why is it sa sobom and not s sobom or s njim?

sa vs s
Both are the same preposition “with”. You usually choose:
- s before most consonants
- sa to make pronunciation easier (e.g. before s, z, some clusters)

S sobom is hard to pronounce (two s sounds together), so people naturally say sa sobom. This is the normal form.

sa sobom vs s njim
- sa sobom – “with himself / herself / oneself” (reflexive; the same person as the subject)
- s njim – “with him” (another person, or you want to highlight that it’s him specifically)

In this sentence, you want “He always carries a bottle of water with him (i.e. on him, with himself)”, so sa sobom is the natural choice:

On stalno nosi bocu vode sa sobom. – He always carries a bottle of water with him (on his person).
On stalno nosi bocu vode s njim. – Sounds like: He always carries a bottle of water with him (another guy) – a different meaning.

What exactly does stalno mean, and how is it different from uvijek?

Both relate to frequency, but with a nuance:

uvijek – always, 100% of the time; more neutral.
- On uvijek nosi bocu vode sa sobom. – He always carries a bottle of water with him.
stalno – literally “constantly”; can mean “all the time” but often implies a bit of annoyance or emphasis on repetition.
- On stalno nosi bocu vode sa sobom. – He’s constantly / always carrying a bottle of water with him.
  Depending on tone, it can sound neutral or slightly like “He’s forever carrying a bottle of water around”.

In many contexts they overlap, and you could safely use either; stalno is slightly more “continuous” or repetitive in flavor.

Can I change the word order, for example: On nosi stalno bocu vode sa sobom or On stalno sa sobom nosi bocu vode?

Yes, Croatian word order is fairly flexible. All of these are grammatically possible, but they differ in emphasis and naturalness:

On stalno nosi bocu vode sa sobom.
– Very natural, neutral emphasis.
Stalno nosi bocu vode sa sobom.
– Also very natural; dropping On. Slightly stronger focus on stalno at the beginning.
On nosi stalno bocu vode sa sobom.
– Possible, but less natural; stresses stalno more strongly (“he constantly carries…”). It can sound a bit clunky in everyday speech.
On stalno sa sobom nosi bocu vode.
– Also okay. Emphasis moves a bit to sa sobom: the fact that he has it on him.
On bocu vode stalno nosi sa sobom.
– More marked word order; stressing bocu vode (that bottle in particular).

Native speakers mostly prefer (1) or (2) unless they’re trying to highlight something specific.

How would the sentence change if the subject were feminine, like “she”?

Only the pronoun changes; the verb nosi stays the same for he/she in the present tense.

On stalno nosi bocu vode sa sobom. – He always carries a bottle of water with him.
Ona stalno nosi bocu vode sa sobom. – She always carries a bottle of water with her.

Everything else (stalno, nosi, bocu vode, sa sobom) remains unchanged.

Is there a difference between sa sobom and kod sebe in this context?

They’re close in meaning but not identical in feel:

sa sobom – literally “with himself/herself”; focuses on having the object on one’s person.
- On stalno nosi bocu vode sa sobom. – He always has the bottle physically with him.
kod sebe – literally “at himself”; often used like “on him / in his possession / at his place”.
- On stalno ima bocu vode kod sebe. – He always has a bottle of water on him / with him.

In your exact sentence:

On stalno nosi bocu vode sa sobom. – emphasizes the carrying.
On stalno ima bocu vode kod sebe. – emphasizes having it on him.

Both are natural, but the verbs differ (nosi vs ima), and sa sobom fits more naturally with nosi.

How is boca declined? I see bocu here and I’d like the full pattern.

Boca (bottle) is a feminine noun ending in -a. Its singular declension:

Nominative: boca – the bottle (subject)
Genitive: boce – of the bottle
Dative: boci – to/for the bottle
Accusative: bocu – the bottle (direct object)
Vocative: boco! – O bottle! (rare, mostly humorous)
Locative: boci – in/on/at the bottle (with prepositions: u boci, na boci)
Instrumental: bocom – with the bottle (colloquial: often bocom, standard: bocom)

In your sentence, it’s bocu because it’s the direct object of nosi.

Is there any difference between saying On stalno nosi bocu vode sa sobom and On uvijek nosi bocu vode sa sobom?

Both are correct and very close in meaning:

On uvijek nosi bocu vode sa sobom. – He always carries a bottle of water with him. (neutral, factual)
On stalno nosi bocu vode sa sobom. – He constantly / always carries a bottle of water with him. (can sound slightly more expressive or even a bit annoyed, depending on intonation)

In many situations you can swap them without changing much, but stalno can add a hint of “non-stop, again and again”.

Could this sentence ever mean “He is constantly wearing a bottle of water with him”? How do we know it’s not progressive like in English?

Croatian doesn’t have a separate present continuous (like English “is carrying”). The simple present nosi covers both:

“he carries / he wears” in general
“he is carrying / he is wearing” right now (depending on context)

However, the presence of stalno (constantly) plus the general nature of the statement makes it clearly habitual here: a regular habit, not just right now.

For a right now meaning, you’d normally add a time phrase:

Sada nosi bocu vode sa sobom. – He is (right now) carrying a bottle of water with him.

In your sentence, everyone will understand it as a habit.

Is there any nuance added by placing stalno in the middle instead of at the beginning: Stalno on nosi bocu vode sa sobom?

Yes, word order affects emphasis:

On stalno nosi bocu vode sa sobom. – neutral: “He always carries a bottle of water with him.”
Stalno on nosi bocu vode sa sobom. – stronger emphasis on on: “It’s always him who carries a bottle of water with him.” (implies contrast with others, or mild irritation)

So Stalno on… sounds like:

complaining about this particular person
or pointing out that he, specifically, is the one who always does this.

Grammatically fine, but more emotionally loaded.