Learn Hardcore Spanish (Latin America): Cuando el agua hierve, comemos pan con mermelada. - When the water boils, we eat bread with jam.

Feminine nouns that start with a stressed “a” or “ha” take the article el in the singular to avoid the “la a” sound: el agua, el águila, el hacha. The noun is still feminine:

Adjectives/pronouns stay feminine: el agua fría, esta agua, mucha agua.
Plural goes back to feminine article: las aguas frías. You’ll also hear the indefinite as un agua (mineral); agreement stays feminine: un agua fría.

Why is the verb form hierve here? How does hervir conjugate?

Hervir is e→ie in the present: yo hiervo, tú hierves, él/ella/Ud. hierve, nosotros hervimos, Uds./ellos hierven. In the preterite and the gerund it’s e→i:

Preterite: hirvió, hirvieron (not “hervió”).
Gerund: hirviendo (“boiling”). Use singular agreement because el agua is grammatically singular.

Could/should it be subjunctive: “Cuando el agua hierva, …”?

Indicative (hierve) for habits/general truths: Cuando el agua hierve, comemos… = “Whenever it boils, we eat…”
Subjunctive (hierva) for a future/pending or directive event: Cuando el agua hierva, comeremos/come… Both are correct but express different time/reference.

Why is there a comma after the “cuando” clause?

When a subordinate clause comes first, Spanish uses a comma: Cuando el agua hierve, …. If the main clause comes first, you usually omit it: Comemos pan con mermelada cuando el agua hierve.

Why not cuándo with an accent?

Accented cuándo appears only in questions/exclamations. Here cuando is a conjunction meaning “when,” so no accent.

Why is nosotros omitted before comemos?

Spanish normally drops subject pronouns because verb endings show the subject. Comemos already means “we eat.” Add nosotros only for emphasis/contrast: Nosotros comemos pan… (ellos no).

Why is there no article before pan? Could it be el pan?

For an unspecified amount, Spanish often uses the bare noun: comemos pan, bebo café. Use el pan for a specific bread or the category as a whole: Comemos el pan que compramos; El pan es barato aquí.

Why con mermelada and not de mermelada?

pan con mermelada = bread with jam (as a topping/served with it).
pan de mermelada = a kind of bread made with or filled with jam (a pastry). For a simple spread, use con.

Does mermelada mean jam or jelly? What about jalea?

In Latin America:

mermelada usually covers what English calls “jam/marmalade” (with fruit pulp/pieces).
jalea is “jelly” (clear, from juice). Some regions also say dulce or compota. Specify the fruit: mermelada de fresa, jalea de uva.

How do you pronounce hierve? Does the h sound? What about the v?

h is silent; it starts like “yer-”.
v sounds like a soft b for most speakers: “YER-beh.”
Stress: hi-ER-ve; mermelada: mer-me-LA-da; agua: A-gua.

Can I switch the word order to “Cuando hierve el agua”?

Yes. Both Cuando el agua hierve, … and Cuando hierve el agua, … are natural. Spanish often puts the subject after the verb in subordinate clauses. Meaning doesn’t change.

If I need a pronoun for agua, is it la or lo?

Feminine: use la. Example: Cuando el agua hierve, la retiro del fuego. The noun is feminine even though it takes el.

How do I say “boiling water” vs. “boiled water”?

agua hirviendo = boiling water (in progress).
agua hervida = boiled water (already boiled).

Why not pan y mermelada? Is there a difference?

pan con mermelada implies the jam is on the bread or eaten together.
pan y mermelada just lists two items; it doesn’t imply one is on the other.

What’s the difference between cuando and si here?

cuando = “when/whenever” (temporal, often assumes it happens).
si = “if” (conditional). Si el agua hierve, comemos… sounds conditional, not simply temporal.

Is “Al hervir el agua, comemos pan con mermelada” okay?

Yes. Al + infinitive means “upon/when [doing].” Al hervir el agua, … is fine. For habits, cuando is more common; for instructions you might also hear En cuanto/Una vez que el agua hierva, … with the subjunctive.