L’eau va bientôt bouillir, alors je prépare les pâtes.

Because French normally shortens la to l’ before a word that starts with a vowel sound. This is called elision.

So:

• la + eau → l’eau

You see the same thing in:

• l’école
• l’amie
• l’heure

French avoids the clash of two vowel sounds here.

This is the near future construction:

• aller in the present tense + infinitive

Here:

• va = aller for elle / il / on
• bouillir = to boil

So l’eau va bouillir literally means the water is going to boil.

The adverb bientôt means soon, so:

• va bientôt bouillir = is going to boil soon

In French, short adverbs like bientôt, déjà, souvent, bien, etc. often go after the conjugated verb and before the infinitive.

So this pattern is very natural:

• va bientôt bouillir
• vais déjà partir
• peut encore attendre

Putting bientôt there sounds normal and idiomatic.

Yes. L’eau bouillira bientôt is also correct.

The difference is mostly one of style and nuance:

• L’eau va bientôt bouillir = more conversational, more immediate, very common in everyday speech
• L’eau bouillira bientôt = simple future, also correct, sometimes a bit more neutral or formal

In ordinary spoken French, the aller + infinitive form is extremely common.

Because the simple present in French often covers what English expresses with the present progressive.

So je prépare les pâtes can mean:

• I prepare the pasta
• I’m preparing the pasta

In this sentence, the context clearly makes it sound like I’m preparing the pasta now.

If you want to stress that the action is happening right at this moment, you can say:

• je suis en train de préparer les pâtes

But that is not required.

This is a common spelling and pronunciation change in some -er verbs.

The infinitive is:

• préparer

But in some forms, the é in the stem changes to è before a silent ending:

• je prépare
• tu prépares
• il / elle prépare
• ils / elles préparent

But:

• nous préparons
• vous préparez

This change helps keep the pronunciation natural.

Here, alors means something like:

• so
• therefore
• then

It links the two parts of the sentence and shows a consequence or logical next step:

• the water is about to boil,
• so I prepare the pasta.

In conversation, alors is very common and can have several uses depending on context.

French usually needs an article before nouns, where English often uses none.

So French prefers:

• les pâtes
• du pain
• la viande

rather than leaving the noun bare.

Here les pâtes sounds natural because it refers to the pasta being prepared for the meal.

A slightly different option would be:

• je prépare des pâtes

That means more like I’m making some pasta.

So:

• les pâtes = the pasta, understood in context
• des pâtes = some pasta

This is an important vocabulary point.

• les pâtes = pasta
• la pâte = dough, pastry, batter, or a paste-like mixture

So:

• Je prépare les pâtes = I’m preparing the pasta
• Je prépare la pâte = I’m preparing the dough

Even though English uses pasta as a singular mass noun, French commonly uses the plural les pâtes.

Bouillir is a tricky word for many learners.

A rough guide is:

• bouillir ≈ boo-yeer

Important points:

• ou sounds like oo
• the ill here does not sound like English l
• the end -ir has the French r, not an English r

So it is closer to boo-yeer than to boo-leer.

The comma is natural and helpful here because the sentence has two linked clauses:

• L’eau va bientôt bouillir
• alors je prépare les pâtes

The comma makes the pause and logic clearer. In informal writing, people do not always punctuate perfectly, but in standard written French this comma is a good choice.