Voda u boci nije bila bistra; bila je mutna i topla.

Because u means in here and expresses a location, so it requires the locative case.

• boca = bottle
• u boci = in the bottle

A very useful rule is:

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

So:

• Voda je u boci. = The water is in the bottle.
• Stavio sam vodu u bocu. = I put the water into the bottle.

Notice the difference:

• boci = locative
• bocu = accusative

Yes. Voda is a feminine noun in Croatian.

Because it is feminine singular, the adjectives that describe it also have feminine singular forms:

• bistra = clear
• mutna = cloudy/murky
• topla = warm

They all end in -a because they agree with voda.

So:

• voda → feminine singular
• bistra / mutna / topla → feminine singular to match it

This kind of agreement is very important in Croatian.

This is the negative past tense of biti (to be) in the feminine singular.

The sentence is talking about voda, which is feminine, so the past participle is bila.

Breakdown:

• je bila = was
• nije bila = was not

More specifically:

• nije = is not / was not as part of the auxiliary construction
• bila = feminine form of been / was

Examples:

• On nije bio. = He was not.
• Ona nije bila. = She was not.
• Voda nije bila bistra. = The water was not clear.

This is a very common Croatian word-order pattern.

In the first clause:

• nije is a fixed negative form, so you get nije bila

In the second clause:

• je is a clitic, and clitics usually go in the second position in the clause
• so Croatian naturally says bila je, not usually je bila, in this kind of sentence

So:

• Voda nije bila bistra = The water was not clear
• bila je mutna i topla = it was cloudy and warm

The second clause leaves out voda because it is already understood.

Because Croatian has no articles like English a or the.

So voda can mean:

• water
• the water

The exact meaning depends on context.

Here, Voda u boci naturally means the water in the bottle, because the phrase u boci makes it specific.

This is normal in Croatian:

• Knjiga je na stolu. = The book is on the table.
• Pas je vani. = The dog is outside.

No article is needed.

Voda is in the nominative case because it is the subject of the sentence.

The sentence is about the water and tells us what it was like:

• Voda ... nije bila bistra
• Voda ... bila je mutna i topla

So:

• voda = nominative singular
• boci = locative singular

This is a basic pattern in Croatian:

• subject → nominative
• object → often accusative
• location after u → locative

Because Croatian, like English, can join adjectives with i (and) when they describe the same noun.

So:

• bila je mutna i topla = it was cloudy and warm

You do not need to repeat the verb:

• natural: bila je mutna i topla
• less natural/redundant: bila je mutna i bila je topla

The shorter version is the normal one.

They are opposites in this context.

• bistra = clear, transparent, not cloudy
• mutna = cloudy, murky, not clear

These words are often used for liquids, especially water.

Examples:

• bistra voda = clear water
• mutna voda = murky/cloudy water

Bistar / bistra / bistro can also be used figuratively in Croatian, like clear-minded or bright, but here it is literal.

Yes, absolutely.

Topla means warm, and it is very commonly used for water, drinks, weather, and objects.

Examples:

• topla voda = warm water
• topao čaj = warm/hot tea
• topla soba = a warm room

In this sentence, topla simply describes the temperature of the water.

Because Croatian often leaves out words that are already clear from context.

The full version could be:

• Voda u boci nije bila bistra; voda je bila mutna i topla.

But that sounds repetitive. Croatian prefers:

• Voda u boci nije bila bistra; bila je mutna i topla.

English does something similar:

• The water in the bottle wasn’t clear; it was cloudy and warm.

Croatian often omits even the equivalent of it if the meaning is obvious.

The semicolon connects two closely related statements.

Here the two parts are:

• Voda u boci nije bila bistra
• bila je mutna i topla

They are strongly connected because the second part explains the first one.

You could also see this written with a comma or as two separate sentences, depending on style:

• Voda u boci nije bila bistra, bila je mutna i topla.
• Voda u boci nije bila bistra. Bila je mutna i topla.

The semicolon gives a slightly more careful, written style.

Yes, in many contexts you can.

• boca = bottle
• flaša = bottle, also very common in everyday speech

So u boci and u flaši can both mean in the bottle.

However, boca is often the more standard or neutral choice, while flaša can sound a bit more colloquial depending on region and context.

Both are useful words to know.

Yes. The key past-tense form here is bila, from biti (to be).

Compare:

• Voda nije bistra. = The water is not clear. (present)
• Voda nije bila bistra. = The water was not clear. (past)

And:

• Voda je mutna i topla. = The water is cloudy and warm.
• Voda je bila mutna i topla. = The water was cloudy and warm.

So bila is what signals the past, together with the auxiliary structure.