Learn Hardcore Indonesian: Kakak perempuan saya juga irit; dia membawa botol air sendiri ke kantor. - My older sister is frugal too; she brings her own water bottle to the office.

kakak = older sibling (gender‑neutral).
perempuan = female/woman. So kakak perempuan = older sister.
If you needed “younger sister,” it’s adik perempuan; older brother is kakak laki‑laki.
Synonyms for “woman”: wanita (more formal), cewek (informal). Here perempuan is neutral and common.

Can I just say kakak saya or kakakku? When should I include perempuan?

kakak saya = my older sibling (gender not specified).
kakakku = my older sibling (using the possessive clitic -ku; more intimate/natural). Spelling doubles the k: kakakku.
Include perempuan only if you need to specify gender or it’s not clear from context.
As a form of address, people say Kak (e.g., Kak Maya). Capitalize Kak when it’s a title/name; otherwise kakak is lowercase.

Where should juga go, and does its position change the meaning?

Default: after the subject — Kakak saya juga irit; Dia juga membawa... (“also”).
Kakak saya irit juga is fine in speech; it slightly emphasizes the predicate.
Dia membawa botol air juga = she brings a water bottle too (in addition to something else).
Dia membawa juga botol air sounds awkward in careful speech.

Is irit the same as hemat or pelit?

irit = frugal/thrifty, uses little. Can describe people and things: motor ini irit bensin.
hemat = economical/saving, often about conserving resources: hemat listrik; berhemat = to economize.
pelit = stingy/cheap (negative).
In your sentence, irit is neutral/positive.

Why is there a semicolon? Could I use a conjunction instead?

The semicolon links two closely related independent clauses.
Natural alternatives:
- Kakak perempuan saya juga irit, jadi dia membawa... (so/therefore)
- Karena dia irit, dia membawa... (because)
- Kakak perempuan saya juga irit. Dia membawa... (two sentences)

Why use dia here? What about ia or beliau? Can the pronoun be dropped?

dia = neutral “he/she”; common in speech and writing.
ia = more formal/literary; usually as subject: Ia membawa... works here.
beliau = respectful “he/she” for elders or respected figures; not for peers in family talk.
Subject drop is possible in conversation when clear: ...; ∅ membawa botol... But keep the pronoun in careful writing.

Is botol air the best term for “water bottle”?

For a reusable personal bottle, botol minum or borrowed tumbler is most natural.
botol air is understandable but can suggest any bottle of water (including disposable).
Safer: ... dia membawa botol minum sendiri ke kantor.

What does sendiri do here? Does it mean “alone”?

After a noun phrase, sendiri = “own”: botol minum sendiri = her own water bottle.
After a verb, sendiri = “by oneself/alone”: Dia membawa sendiri botol itu = she carried it herself (without help).
As an intensifier of a pronoun: dia sendiri = she herself.

Why ke kantor and not di kantor?

ke = to/toward (destination): membawa ... ke kantor = bring ... to the office.
di = at/in (location): Dia minum dari botolnya di kantor = she drinks from her bottle at the office.
membawa ... di kantor is ungrammatical; use ke for motion.

How can I say “her (own) water bottle” more explicitly?

Add the possessive clitic and sendiri: Dia membawa botol minumnya sendiri ke kantor.
Or with milik (more formal): ... botol minum miliknya.
Without sendiri, botol minumnya is just “her water bottle” (no emphasis on “own”).

Can I use bawa instead of membawa? What about membawakan?

Dia bawa... is very common in casual speech; in formal writing prefer membawa.
membawakan = bring something for someone / perform (a song, etc.). Different: Dia membawakan kakaknya botol air = she brought her older sibling a water bottle.

What are some natural alternative ways to say the whole sentence?

Kakakku juga hemat; ia membawa botol minum sendiri ke kantor.
Kakak perempuan saya juga irit, jadi dia membawa botol minumnya sendiri ke kantor.
Karena irit, kakak saya selalu membawa tumbler sendiri ke kantor.
Kakak saya pun irit; dia bawa botol minum sendiri ke tempat kerja.