Pokraj kuće je stari bunar, ali sada vodu uzimaju iz slavine.

Because pokraj is a preposition that normally takes the genitive case.

• kuća = nominative singular, house
• kuće = genitive singular, of the house / by the house in this kind of expression

So:

• pokraj kuće = next to the house / beside the house

This is something you often have to memorize with Croatian prepositions: each preposition usually requires a specific case.

Pokraj means beside, next to, or by.

It is very close in meaning to kraj, and in many everyday sentences they can sound almost interchangeable:

• pokraj kuće = beside the house
• kraj kuće = by the house

Pokraj can sound a little more explicitly spatial, but in normal usage both are common.

This is because je is a clitic in Croatian. Clitics are short unstressed words that tend to go in the second position of the clause.

So in:

• Pokraj kuće je stari bunar

the first unit is Pokraj kuće, and je comes right after it.

A more English-like order such as Stari bunar je pokraj kuće is also possible, but it shifts the emphasis a bit. The original sentence starts by setting the scene: Beside the house...

Because the adjective has to agree with the noun in gender, number, and case.

Here:

• bunar is masculine singular nominative
• so the adjective must also be masculine singular nominative
• therefore: stari bunar = old well

Compare:

• stara kuća = old house
• staro selo = old village
• stari bunar = old well

Croatian often uses to be in a simpler way than English.

• Pokraj kuće je stari bunar literally looks like Beside the house is an old well
• natural English is There is an old well beside the house

So Croatian does not need a separate dummy subject like there. The verb je simply means is, and the existence meaning comes from the whole sentence structure.

Because vodu is the accusative singular form, and it is the direct object of uzimaju.

• voda = nominative, water
• vodu = accusative, used when water is the thing being taken

So:

• uzimaju vodu = they take/get water

This is a very common pattern in Croatian: the direct object usually goes in the accusative.

Because the preposition iz always takes the genitive case.

• slavina = nominative singular, tap/faucet
• slavine = genitive singular

So:

• iz slavine = from the tap

This is parallel to:

• iz kuće = from the house
• iz grada = from the city

Croatian often omits subject pronouns when the verb ending already shows the person and number.

• uzimaju = they take / they get

So the sentence does not need oni. The verb form itself tells you it is third person plural.

Also, in sentences like this, they can be understood in a general sense, like:

• people in the house
• the residents
• people in general

English sometimes also does this with they.

Yes, uzimati / uzeti basically means to take, but in context it can also mean get or draw.

So:

• vodu uzimaju iz slavine literally = they take water from the tap
• natural English = they get their water from the tap

This sounds normal in Croatian. It contrasts the old well with the modern water source.

Yes. Then it would simply mean There is a well beside the house.

The adjective stari adds useful information and also helps create a contrast with the second part:

• there is an old well
• but now they use the tap

So stari is not grammatically necessary, but it is meaningful in the sentence.

Ali means but, and sada means now.

Together they introduce a contrast:

• Pokraj kuće je stari bunar = There is an old well beside the house
• ali sada vodu uzimaju iz slavine = but now they get water from the tap

So the idea is:

• the well still exists
• but it is no longer the usual source of water

Not completely. Croatian word order is fairly flexible, although some versions sound more natural depending on emphasis.

The original:

• ali sada vodu uzimaju iz slavine

is perfectly natural.

You could also hear:

• ali sada uzimaju vodu iz slavine
• ali vodu sada uzimaju iz slavine

The differences are mostly about emphasis and information flow, not basic meaning. Croatian uses word order more freely than English, but not randomly. Speakers move parts around to highlight what is new, contrasted, or important.