Ova rupa za odvod je premala.

Because rupa is a feminine singular noun, and Croatian words like this must agree with the noun’s gender, number, and case.

So in the nominative singular:

• ovaj = this (masculine)
• ova = this (feminine)
• ovo = this (neuter)

Since rupa is feminine, you say ova rupa = this hole.

They match each other grammatically.

In Croatian, adjectives agree with the noun they describe. Here, rupa is feminine singular, so the adjective also has to be feminine singular:

• rupa je premala = the hole is too small

If the noun were masculine or neuter, the adjective would change too:

• odvod je premalen / premali = the drain is too small
• otvor je premalen / premali = the opening is too small
• crijevo je premalo = the pipe/tube is too small

So the -a ending here shows feminine singular agreement.

Literally, it means for drainage or for a drain.

• za = for
• odvod = drain, drainage, outflow

So rupa za odvod is literally a hole for drainage / a hole for a drain, which in natural English is something like drain hole or drainage hole.

It is in the accusative singular.

The preposition za usually takes the accusative when it means for. So:

• za odvod

Here, odvod is a masculine inanimate noun, and for masculine inanimate nouns, the accusative singular is often the same as the nominative singular. That is why it still looks like odvod.

Because pre- is a prefix attached directly to the adjective.

• mala = small
• premala = too small

This pre- often means too, overly, excessively in this kind of word:

• skup → preskup = too expensive
• daleko → predaleko = too far
• velik → prevelik = too big

So premala is the normal one-word way to say too small.

They are very close, but premala is the more natural, compact everyday choice here.

• premala = too small
• previše mala = excessively small / too small

In a simple statement like this, premala is the most idiomatic form.

Because Croatian does not have articles like English a and the.

Whether something is definite or indefinite is understood from context, or shown in other ways. In this sentence, ova already tells you it is this hole, so the meaning is definite without needing an article.

Because je is an unstressed form, called a clitic, and Croatian usually places clitics near the beginning of the sentence, after the first main unit or phrase.

Here the first unit is the whole subject:

• Ova rupa za odvod = this drain hole

Then comes:

• je = is

So the sentence structure is perfectly natural: Ova rupa za odvod je premala.

Yes. Odvodna rupa is also possible and may sound more compact.

So you may hear both:

• rupa za odvod = hole for drainage / drain hole
• odvodna rupa = drainage hole / drain hole

The sentence you were given is completely natural, but Croatian often allows more than one way to build this kind of noun phrase.

Yes, Croatian word order is more flexible than English word order.

The given sentence is a neutral, natural way to say it:

• Ova rupa za odvod je premala.

But you could also move things for emphasis, for example:

• Premala je ova rupa za odvod.

That version puts more focus on premala. So the basic meaning stays the same, but the emphasis changes.

In most cases, yes: nouns ending in -a are very often feminine in Croatian, and rupa is one of them.

That is why you get feminine agreement:

• ova rupa
• mala rupa
• rupa je premala

There are some exceptions in Croatian, especially with nouns referring to male people, but as a general rule, -a often signals a feminine noun.