Izljev vode je problem.

Because vode is in the genitive singular.

In izljev vode, the second noun tells you what is flowing/spilling/out. Croatian often uses this pattern:

• izljev vode = an outflow/spill of water
• čaša vode = a glass of water
• boca vina = a bottle of wine

So voda changes to vode because it depends on izljev.

Izljev is in the nominative singular.

It is the subject of the sentence:

• Izljev vode = the subject
• je = is
• problem = predicate noun

So the basic structure is:

[subject] + [is] + [noun/complement]

Because after je (is), Croatian often uses the nominative for a predicate noun in simple identification statements.

So:

• Izljev vode je problem.
• literally: A water outflow/spill is a problem.

Here problem stays in its dictionary form, which is nominative singular.

Je is the 3rd person singular present tense of biti (to be).

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In this sentence, the subject izljev vode is singular, so Croatian uses je:

• Izljev vode je problem. = A water spill is a problem.

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

So problem can mean:

• a problem
• the problem

The exact meaning depends on context.

Likewise, izljev vode could be understood as:

• a water spill/outflow
• the water spill/outflow

English requires an article, but Croatian does not.

Here are the genders:

• izljev — masculine
• voda — feminine
• problem — masculine

Gender matters because it affects adjective endings, pronouns, and some other forms.
In this sentence there are no adjectives, so you do not see much agreement yet, but the genders are still important to know.

For example:

• velik izljev vode = a big water outflow/spill
• ozbiljan problem = a serious problem

Both velik and ozbiljan are in masculine form because they agree with izljev and problem.

The sentence can be rearranged, although the most neutral order is:

• Izljev vode je problem.

You could also say:

• Problem je izljev vode.

That shifts the focus a little, roughly like The problem is the water outflow/spill.

Croatian word order is more flexible than English because cases help show the grammatical relationships.

A useful approximation is:

• izljev ≈ EEZ-lyev

The tricky part is lj, which is a single Croatian sound, similar to the lli in some pronunciations of million, but not exactly the same in all dialects of English.

Also:

• v in Croatian is usually pronounced clearly, like English v
• j is pronounced like English y

So je sounds like yeh.

It is grammatical, but whether it sounds natural depends on context.

Izljev vode is understandable, but in everyday speech Croatian speakers might sometimes prefer a more specific or more common expression depending on the situation, for example words meaning leak, spillage, or flooding.

So this sentence is fine for learning grammar, especially:

• noun + genitive (izljev vode)
• je = is
• predicate noun (problem)

But in real life, the most natural wording may vary with context.

In this sentence, vode is understood as genitive singular of voda.

Formally, vode can also be another grammatical form in Croatian in other contexts, but here the meaning is clearly:

• izljev vode = outflow/spill of water

So a learner should read it here as of water, not as a plural meaning.

You can use that as a grammar guide, but it is not natural English.

A word-for-word breakdown is:

• izljev = outflow / spill
• vode = of water
• je = is
• problem = problem

Natural English would usually be something like:

• A water spill is a problem.
• Water leakage is a problem.
• A water outflow is a problem.

The best translation depends on the context and the exact meaning intended by izljev.