Learn Hardcore Indonesian: Keluarga kami bekerja sama melawan banjir kecil di halaman belakang. - Our family works together to fight the small flood in the backyard.

keluarga kami = our family (but not yours) – for example, you’re talking about your own family to a friend who is not part of that family.
keluarga kita = our family (yours and mine) – for example, siblings talking to each other about their parents and siblings.

In the sentence, keluarga kami suggests the listener is not part of that family.

Is bekerja sama one word or two, and how is it different from kerja sama?

Modern standard Indonesian usually writes it as two words:

kerja sama (noun) = cooperation, collaboration
- e.g. Kami menghargai kerja sama Anda. = We appreciate your cooperation.
bekerja sama (verb) = to cooperate, to work together
- e.g. Mereka bekerja sama. = They work together.

In your sentence, bekerja sama is a verb: our family works together / our family cooperates.

You may sometimes see bekerjasama as one word in informal writing, but the recommended form is bekerja sama.

Is bekerja sama the same as bekerja bersama-sama or gotong royong?

They are related but not identical:

bekerja sama – neutral: to cooperate, work together (general, can be formal or informal).
bekerja bersama-sama – more literally “work together-together”; sounds a bit more descriptive/emphatic, but also a bit wordy.
gotong royong – culturally loaded term: mutual help / community effort, usually for physical or social tasks (cleaning, building, dealing with floods, etc.).

For this context, a very natural alternative would be:

Keluarga kami gotong royong melawan banjir kecil di halaman belakang.

This emphasizes the communal, hands-on teamwork aspect.

Does melawan really mean “fight”? Is it natural to say you “fight” a flood in Indonesian?

Yes, melawan literally means to fight / to oppose / to go against. It’s commonly used for:

fighting an enemy: melawan musuh
resisting something: melawan arus (go against the current)
fighting problems: melawan penyakit, melawan kemiskinan

So melawan banjir kecil can be understood as fighting/struggling against a small flood, and it doesn’t sound strange.

However, other verbs are sometimes more natural, depending on nuance:

mengatasi banjir kecil – to deal with / overcome the small flood
menanggulangi banjir – to handle / tackle the flood (more formal/technical)
menghadapi banjir – to face / deal with the flood

Your sentence is fine; melawan just makes it sound a bit vivid or dramatic, like actively battling the water.

Why is it banjir kecil and not something like sedikit banjir?

Because kecil and sedikit are different:

kecil = small in size / degree
- banjir kecil = a small / minor flood
sedikit = a little / a small amount (quantity)
- sedikit air = a little water
- sedikit banjir is not natural; it sounds like “a little bit of flood”, which Indonesians don’t usually say.

So banjir kecil is the correct way to say a small (minor) flood.

Can I say sebuah banjir kecil instead of banjir kecil?

You can, but it’s usually not necessary.

banjir kecil – already works as a small flood / some minor flooding.
sebuah banjir kecil – literally a (single) small flood; grammatically correct, but sounds a bit heavier or more literary in many contexts.

Indonesian often omits words like a / an / the, so banjir kecil is the most natural choice in everyday language.

Why are the adjectives after the nouns, like banjir kecil and halaman belakang?

Because in Indonesian, the normal pattern is:

Noun + Adjective

Examples:

rumah besar = big house
kucing hitam = black cat
banjir kecil = small flood
halaman belakang = back yard / backyard

Putting the adjective before the noun (kecil banjir, belakang halaman) is ungrammatical in standard Indonesian.

What does halaman belakang literally mean, and is it the usual way to say “backyard”?

Literally:

halaman = yard, courtyard, yard area in front/around a house
belakang = back, behind

So halaman belakang = back yard, i.e. the yard at the back (of the house).

This is a very common and natural way to say backyard.

Other related phrases:

halaman depan = front yard
belakang rumah = behind the house (more general, not necessarily a proper yard)

Why do we use di in di halaman belakang?

di is the basic preposition for location: at / in / on, depending on context.

di rumah = at home
di sekolah = at school
di halaman belakang = in/at the backyard

You could technically use pada in some very formal or written contexts, but:

di halaman belakang is the normal, natural way to say in the backyard in everyday language.

Can the location part di halaman belakang be moved to the beginning of the sentence?

Yes. Indonesian word order is flexible, and moving the location to the front just changes emphasis slightly:

Keluarga kami bekerja sama melawan banjir kecil di halaman belakang.
→ neutral: stating what the family did, then where.
Di halaman belakang, keluarga kami bekerja sama melawan banjir kecil.
→ emphasizes the place first: In the backyard, our family worked together...

Both are grammatically correct.

Why is it keluarga kami and not something like keluargaku?

Both are possible, but they have different possessors:

keluarga kami = our family (we/us – excluding the listener)
keluargaku = my family (only me)

Use:

keluarga kami when you want to talk about the family as belonging to the group “we” (maybe you and your siblings, etc.).
keluargaku when you emphasize yourself as one person.

Your sentence presents the family as a group belonging to a plural we, so keluarga kami fits well.

There’s no word for “are / were” in the sentence. How do we know the tense?

Indonesian verbs do not change form for tense. There is no direct equivalent of English am / is / are / was / were / will be here.

Keluarga kami bekerja sama melawan banjir kecil di halaman belakang can mean:

Our family works together against a small flood in the backyard (present/general)
Our family worked together against a small flood in the backyard (past)

Tense is understood from context or from time words, for example:

Kemarin keluarga kami bekerja sama... = Yesterday our family worked together...
Sekarang keluarga kami bekerja sama... = Now our family is working together...

Is this sentence formal, informal, or neutral in style?

It’s basically neutral, slightly leaning towards standard / written style:

Uses standard vocabulary (keluarga, bekerja sama, melawan, banjir, halaman belakang).
No slang or overly formal bureaucratic words.

In spoken, casual Indonesian, people might say something like:

Kami sekeluarga gotong royong mengatasi banjir kecil di belakang rumah.

But your original sentence is perfectly natural in narratives, essays, or standard speech.

What are the root words and prefixes in bekerja sama and melawan?

Breaking them down:

bekerja sama
- Root: kerja = work
- With prefix ber- → bekerja = to work
- Plus sama = same / together
  → bekerja sama = to work together, to cooperate
melawan
- Root: lawan = opponent / enemy / opposite
- With prefix me- → melawan = to oppose, to fight against

Indonesian often uses me-, ber-, etc. to turn roots into verbs.

How do you pronounce the tricky parts like kerja, banjir, and halaman?

Key points:

c in Indonesian is pronounced like “ch” in “church” (not in this sentence, but useful generally).
j is like “j” in “judge”.

Specific words:

kerja → kuhr-jah (j as in judge)
banjir → bahn-jeer (again j as in judge)
halaman → ha-lah-man (each vowel clearly: a like father)

Stress tends to be on the second-to-last syllable:

ke-RJA, BAN-jir, ha-LA-man.