Quello di cui Marta ha voglia a luglio, quando torna dalla piscina, è solo un bicchiere d’acqua e un po’ d’uva.

A useful way to split it up is:

• Quello di cui Marta ha voglia a luglio, quando torna dalla piscina = the subject
• è = the main verb
• solo un bicchiere d’acqua e un po’ d’uva = what that subject is identified as

So the whole sentence is built like:

• What Marta feels like having in July, when she comes back from the pool, is just a glass of water and some grapes.

The long part before è is normal Italian sentence structure: the subject can be quite long.

Here quello does not literally mean just that one. It is being used as a pronoun meaning:

• what
• that which
• the thing that

So Quello di cui Marta ha voglia... means What Marta feels like... or The thing Marta wants...

This use of quello is very common in everyday Italian.

Because the expression is avere voglia di qualcosa = to feel like something / to want something.

The verb phrase requires the preposition di. Once you turn that idea into a relative clause, the di has to stay:

• Marta ha voglia di un bicchiere d’acqua
• Quello di cui Marta ha voglia...

So cui is used after a preposition, and here that preposition is di.

Because che cannot replace a phrase that needs a preposition in this kind of structure.

You can say:

• La cosa che Marta vuole = the thing that Marta wants

But with avere voglia di, the di is part of the expression, so you need:

• La cosa di cui Marta ha voglia

Not:

• La cosa che Marta ha voglia

That would be ungrammatical in standard Italian.

Avere voglia di is a very common Italian expression meaning:

• to feel like
• to want
• to be in the mood for

It can be followed by:

• a noun: Ho voglia di pizza
• an infinitive: Ho voglia di dormire

In this sentence, it is followed by things Marta wants:

• un bicchiere d’acqua
• un po’ d’uva

Compared with volere, avere voglia di often sounds more like a craving, desire, or inclination.

In Italian, months are usually used without an article, and a is the normal preposition for in with months:

• a luglio = in July
• a maggio = in May
• a dicembre = in December

A more specific expression like nel luglio del 2024 means in July 2024, referring to a particular July rather than July in general.

Because Italian often uses the present tense for habitual or repeated situations.

Here quando torna dalla piscina means:

• when she comes back from the pool
• or more naturally in context, whenever she comes back from the pool

The sentence is describing a regular situation in July, not one single completed event.

Dalla is the contraction of da + la.

• da = from
• la piscina = the swimming pool
• dalla piscina = from the swimming pool / from the pool

With tornare, da is commonly used to say where someone is coming back from:

• torna da scuola = she comes back from school
• torna dal lavoro = she comes back from work
• torna dalla piscina = she comes back from the pool

Because the grammatical subject is not un bicchiere d’acqua e un po’ d’uva. The subject is the whole singular idea:

• Quello di cui Marta ha voglia...

That whole phrase is treated as singular: that thing / what she wants.

So Italian uses:

• è

not:

• sono

If you changed the subject to a plural one, then the verb would be plural:

• Le cose di cui Marta ha voglia sono...

This is elision of di before a vowel.

• di acqua becomes d’acqua
• di uva becomes d’uva

This is very common after words of quantity or container:

• un bicchiere d’acqua
• un litro d’olio
• un po’ d’uva

It makes the phrase sound natural and fluid.

Because uva in Italian is often treated as a collective or mass noun, where English prefers the plural grapes.

So:

• un po’ d’uva = some grapes
• mangiare uva = to eat grapes

Italian often uses singular uva where English uses a plural noun. If you want to be more specific, you can also talk about bunches:

• un grappolo d’uva = a bunch of grapes

Here solo limits the whole thing Marta wants:

• è solo un bicchiere d’acqua e un po’ d’uva

So the meaning is:

• all she wants is just a glass of water and some grapes

It is not emphasizing one single glass. If you wanted to emphasize the number one, you might say:

• un solo bicchiere d’acqua

That would mean only one glass of water. Here, solo applies to the entire phrase that follows.