Según la fontanera, la gotera empeora cuando llueve.

Según is a preposition meaning according to / as per.
Según la fontanera literally means according to the plumber (female) and works like an “attribution” phrase: the speaker is reporting information coming from that person, not necessarily stating it as their own proven fact.

In Spain, fontanero / fontanera is the standard word for plumber.
Plomero / plomera is common in much of Latin America, but in Spain it can sound non‑standard or regional/foreign. If you’re aiming for Spain Spanish, fontanera is the most natural choice.

Spanish normally uses the definite article with professions when referring to a specific person: la fontanera = the plumber (the one we’re talking about).
Without the article, it usually sounds like you’re naming someone’s profession after ser (e.g., Ella es fontanera) or using it in certain headlines/labels. Here, it’s a specific plumber, so la is expected.

Gotera is a leak that drips (from a ceiling, pipe joint, roof, etc.), emphasizing the dripping.
Fuga is a broader word meaning a leak/escape (gas leak, water leak, etc.) and doesn’t necessarily imply dripping.
So gotera is very common for the everyday “drip leak” problem in a home.

La gotera suggests a specific leak already known in the conversation/context: the leak (the one in your house).
Una gotera would introduce it as a leak (one leak among others, or mentioned for the first time with less “shared context”).

The present tense here expresses a general, repeated, or typical pattern: the leak gets worse whenever it rains.
If you wanted to describe a one‑off situation in the past, you’d use past tenses (e.g., empeoró cuando llovió = it got worse when it rained that time).

It can mean both depending on whether it’s used intransitively or transitively:

• Intransitive: La gotera empeora = The leak gets worse.
• Transitive: La lluvia empeora la gotera = The rain makes the leak worse.
  In your sentence, it’s intransitive because there’s no direct object after empeora.

With cuando, Spanish uses:

• Indicative (llueve) for habitual or known patterns: when(ever) it rains (as a regular condition).
• Subjunctive (llueva) for future/uncertain events: when it rains (in the future) / whenever it may rain.

So empeora cuando llueve describes a recurring fact. If you were talking about a future situation, you might say: Empeorará cuando llueva (It will get worse when it rains).

Yes, and it’s very natural:

• Según la fontanera, la gotera empeora cuando llueve.
• Según la fontanera, cuando llueve, la gotera empeora.

The meaning is essentially the same. The second version puts more emphasis on the condition cuando llueve by placing it earlier.

The comma separates an introductory “source” phrase (Según la fontanera) from the main statement. It improves readability and is standard punctuation in Spanish when you start with an attributive phrase like según X, en mi opinión, por lo visto, etc.

Según is stressed on the second syllable: se-GÚN.
The accent mark shows the stress falls on -gún, which is not the default stress pattern for a word ending in n (normally stress would fall on the penultimate syllable).

Yes:

• Según la fontanera, ... sounds a bit more like reporting or citing her view/information (slightly more detached).
• La fontanera dice que... is more direct: the plumber says that...

Both are correct; según often feels more like “as per her assessment” and can subtly distance the speaker from endorsing it as certain fact.