Badekaret lekker litt, så jeg ringer vaktmesteren.

Badekaret is the definite form (“the bathtub”).

• et badekar = “a bathtub” (indefinite, neuter noun)
• badekaret = “the bathtub” (definite: -et ending is typical for neuter nouns)
  So the sentence refers to a specific bathtub the speaker has in mind.

Badekar is a neuter noun (it takes et in the indefinite form). Gender matters because it affects:

• the article: et badekar (not en)
• the definite ending: badekar-et
• adjectives/pronouns that agree with it in other sentences (e.g., et stort badekar = “a big bathtub”).

Yes—lekker is the present tense of å lekke (“to leak”). It’s closely related in meaning to English leak, though the words aren’t just direct copies.

• Badekaret lekker = “The bathtub is leaking.”

Norwegian commonly uses the simple present for actions happening now (like English present continuous).

• Badekaret lekker can mean “is leaking” (right now / currently)
• jeg ringer can mean “I’m calling” / “I call” depending on context
  If you want to emphasize “right now,” you can add nå: Badekaret lekker litt, så jeg ringer vaktmesteren nå.

litt means “a little” or “slightly.” It softens the statement: it’s leaking, but not necessarily a lot.

• lekker litt = “leaks a little” / “is leaking slightly”
  You could contrast it with mye (“a lot”): Badekaret lekker mye.

Because så here introduces a result/consequence (“so”), and Norwegian typically uses a comma to separate the two clauses:

• Badekaret lekker litt, så jeg ringer vaktmesteren.
  This is very common in Norwegian writing.

Yes, så has several uses. Here it functions like “so” = therefore/as a result.
Other common uses:

• så = “then” in sequences: Først spiser vi, så drar vi. (“First we eat, then we leave.”)
• så in degree expressions: så stor (“so big”), så lenge (“so long”).

This is a key word-order point: when så means “so/therefore” and works like a linking adverb between clauses, Norwegian often uses V2 word order in the second clause—meaning the verb comes in the second position, which can force the subject after the verb:

• Badekaret lekker litt, så ringer jeg vaktmesteren. (very common)
  But your sentence has så jeg ringer ..., which is also used—especially when så is interpreted more like “so (that)” / “so I...” in a slightly more spoken, flowing style.
  If you’re learning a reliable rule: after many connecting adverbs, Norwegian frequently prefers så + verb + subject (så ringer jeg ...).

Both are possible, but they mean slightly different things:

• jeg ringer vaktmesteren = “I’m calling / I call (as a result)” (immediate, matter-of-fact)
• jeg skal ringe vaktmesteren = “I’m going to call the caretaker” (intention/future)
  In this context (leak → action), the present tense sounds direct and natural.

A vaktmester is typically a caretaker/janitor/maintenance person for a building (often in an apartment complex, school, office building). They handle general maintenance and coordinate repairs.
A plumber is en rørlegger. If you know it’s a plumbing job, you might say:

• Badekaret lekker, så jeg ringer rørleggeren.
  But in many buildings you contact the vaktmester first.

vaktmesteren means “the caretaker”—usually a specific one that belongs to the building or that both speaker and listener can identify.

• en vaktmester = “a caretaker” (any one)
• vaktmesteren = “the caretaker” (the known/expected one)

A rough guide (pronunciation varies by dialect):

• Badekaret: stress often on the first syllable: BA-de-ka-ret
• lekker: like LEK-ker (short e sound)
• litt: short vowel, crisp t: litt
• ringer: RING-er (Norwegian r varies a lot by region)
• vaktmesteren: VAKT-mes-te-ren (often a clear t in vakt, and stress early)

Yes. derfor is closer to “therefore” and it strongly triggers the common V2 order:

• Badekaret lekker litt, derfor ringer jeg vaktmesteren.
  This can sound slightly more formal than så in everyday speech/writing.