Learn Hardcore Spanish (Latin America): En la fila, mi novio compra agua mientras yo reviso lo que falta de mis apuntes. - In line, my boyfriend buys water while I check what is missing from my notes.

Spanish often uses the simple present for actions happening right now, especially when context makes it clear. So Mi novio compra agua can mean “My boyfriend is buying water (now).” The progressive (está comprando/estoy revisando) is also correct, but it emphasizes the ongoingness at this very moment. Either works here; the simple present is just more neutral and common.

Is the subject pronoun yo necessary in mientras yo reviso?

No. Spanish usually drops subject pronouns. Mientras reviso is perfectly fine. Adding yo emphasizes the subject change (from mi novio to yo) or adds slight contrast.

Why lo que and not just que in lo que falta?

Lo que means “what/that which” and is used when there’s no specific noun stated beforehand. You’d use que only if there is an explicit antecedent:

Lo que falta = “what is missing.”
Las partes que faltan = “the parts that are missing.”

Why is it falta (singular) and not faltan?

Because the grammatical subject is lo que (neuter singular: “what”), so the verb is singular: lo que falta. If you specify a plural antecedent, you use plural: las cosas que faltan.

How does the verb faltar work, and could it be me falta here?

Faltar means “to be missing/lacking/left.” It often uses an indirect object to mark who is affected:

Me falta tiempo. = I’m missing time.
Nos faltan datos. = We lack data.

In your sentence, lo que falta is impersonal (“what is missing”). You could also say:

Reviso lo que me falta en mis apuntes. (what I’m missing in my notes)

Why de mis apuntes and not en mis apuntes?

Both can work but convey a slightly different feel:

lo que falta de mis apuntes = what is missing from my notes (source/ownership perspective).
lo que falta en mis apuntes = what is missing in my notes (location/internal perspective).

For missing information within a document, en is very common. Your original is acceptable too.

Why use apuntes instead of notas for “notes”?

Across much of Latin America, apuntes is the standard for class/study notes. Notas can mean “grades/marks” or short notes/annotations, depending on country. Apuntes is the safest choice for “class notes.”

Why is there no article before agua in compra agua?

Spanish often omits the article with mass/uncountable nouns when speaking generally or nonspecifically:

compra agua = buys water (some water, water in general). Use an article when specific or countable:
compra el agua (the specific water we mentioned)
compra un agua (a water = a bottle/glass/serving)

If agua is feminine, why do I sometimes see el agua?

Agua is feminine, but with singular nouns that begin with a stressed “a,” Spanish uses the masculine article el to avoid the “la a–” sound clash:

el agua fría (note the adjective stays feminine: fría)
Plural reverts to feminine: las aguas frías
With other determiners, keep feminine: esta agua, mucha agua, toda esta agua
With the indefinite, standard is also masculine: un agua (mineral)

Can I say una agua?

You may hear una agua in some places (especially when “a water” means a serving), but standard usage prefers un agua with singular stressed-a nouns: un águila, un hacha, un agua. In any case, when you mean water in general, you typically use no article: quiero agua.

Does novio always mean “boyfriend”? What about fiancé/partner?

novio/novia = boyfriend/girlfriend, and also fiancé/fiancée (context clarifies).
esposo/esposa = husband/wife.
Gender-neutral option: pareja (partner).
Regional terms exist (e.g., pololo/polola in Chile, enamorado/a in parts of Peru), but novio/novia is widely understood.

Is En la fila the most natural way to say “in line” in Latin America?

Yes, en la fila is very natural. You’ll also hear:

en la cola (widely used; “cola” also means “tail,” and informally “butt,” but context makes it clear)
haciendo fila/cola = “standing in line.”
Your original En la fila works well to set the scene.

Could I write Haciendo fila, mi novio compra agua…?

Yes, but be careful: Haciendo fila makes the subject of the gerund the same as the main clause’s subject. Since the subject is mi novio, it reads as “While he is in line, my boyfriend buys…,” which is fine. If you wanted both of you to be in line, En la fila is safer and more neutral.

Why use mientras and not cuando or durante?

mientras = “while,” emphasizes simultaneity of two actions.
cuando = “when,” not focused on simultaneity; it marks a time point or period.
durante
- noun = “during” + a time period (not a clause), e.g., durante la fila (less idiomatic than en la fila).

Also note: mientras que often means “whereas” (contrast). Mientras can take the subjunctive when it means “as long as” (condition):

Estudia mientras tengas tiempo. (as long as you have time)

Is the comma after En la fila required?

It’s optional. A short introductory phrase like En la fila can take a comma for clarity, but En la fila mi novio compra… is also correct. Use the comma if it helps readability.

Is revisar the best verb here? What about repasar, checar/chequear, or ver?

revisar = to check/examine/verify (good when you’re checking what’s missing).
repasar = to go over/review (study sense).
checar/chequear = widely used in Latin America but considered informal/anglicism in some contexts.
ver = to see/check (very general).
Your choice of revisar lo que falta is natural.

Could I say mis notas instead of mis apuntes?

Depending on the country, notas might be understood as “grades/marks.” It can mean “notes” in some regions, but apuntes is the clearest, most widely understood word for class notes.

Any pronunciation tips for key words?

fila: FEE-la
novio: NOH-byoh (the “v” is like a soft “b”)
agua: AH-gwa (hard “g”)
mientras: MYEN-tras (the “ie” forms a single glide)
reviso: reh-VEE-so
falta: FAHL-ta
apuntes: ah-POON-tes

Stress falls where shown in caps.