O menino saltou à água.

O is the masculine singular definite article, meaning the.

It matches menino, which is a masculine singular noun:

• o menino = the boy

In Portuguese, articles are used very often, sometimes more often than in English.

Menino means boy, and menina means girl.

This is a gender difference in the noun:

• o menino = the boy
• a menina = the girl

The article changes too:

• o with masculine nouns
• a with feminine nouns

Saltou is the pretérito perfeito in Portuguese, which is often called the simple past or preterite in English grammar explanations.

It comes from the verb saltar = to jump.

So:

• eu saltei = I jumped
• tu saltaste = you jumped
• ele/ela saltou = he/she jumped

In this sentence, saltou means jumped.

Because saltar is an -ar verb, and in the preterite, the ele/ela/você form usually ends in -ou.

For example:

• falar → falou
• entrar → entrou
• saltar → saltou

So saltou tells you:

• the action happened in the past
• the subject is he, she, or you (formal)

Here, the subject is o menino, so he jumped.

À is a contraction of:

• a (preposition)
• a (feminine singular definite article)

So:

• a + a = à

In this sentence, à água is literally something like to the water, but the natural English meaning is usually into the water.

The grave accent in à is important because it shows this contraction.

Because à and a are different things.

• a can be just a preposition, or just the feminine article
• à specifically shows the contraction of a + a

So:

• Vou a casa is wrong in standard Portuguese for I’m going home
• Vou à casa da minha avó = I’m going to my grandmother’s house

In your sentence:

• saltou à água = jumped into the water

The accent is not a stress mark here in the usual sense; it mainly marks the contraction.

Because água is a noun, and in Portuguese it often appears with an article when introduced by certain prepositions or in normal noun phrases.

Here the full form behind à is:

• a água

So the sentence contains the idea of to the water / into the water, with the feminine article included.

Also, água is feminine:

• a água

Even though it begins with a stressed a, it is still feminine.

Because água is grammatically feminine.

Some learners get confused because words beginning with a can look unusual with articles, but the gender is still feminine:

• a água fria = the cold water
• esta água = this water

Notice that adjectives and determiners also show feminine agreement:

• água fria, not água frio

Not exactly.

A useful distinction is:

• saltou à água = jumped into the water
• saltou na água = jumped in the water / jumped while in the water

In many contexts, à água strongly suggests movement from outside to inside the water.

So if the boy was on a rock or at the poolside and then jumped into the water, saltou à água is very natural.

Yes, para a água is possible and understandable.

But there is a nuance:

• saltou à água is a compact, idiomatic way to say jumped into the water
• saltou para a água can sound a bit more like jumped toward the water or simply a less fixed expression, depending on context

In European Portuguese, saltar à água is a very natural expression for entering the water by jumping.

This is the normal basic Portuguese word order:

subject + verb + complement

• O menino = subject
• saltou = verb
• à água = complement

This is the most neutral and natural order.

Portuguese can change word order for emphasis, but this sentence is the standard, straightforward version.

In European Portuguese, menino is pronounced approximately like:

muh-NEE-noo

A few details:

• the unstressed e in the first syllable is often reduced, sounding a bit like uh
• the stress is on ni
• the final o in European Portuguese is often a reduced oo-like sound, not a full English oh

So it does not sound exactly like Brazilian Portuguese.

Approximately, in a learner-friendly way:

sal-TOH ah AH-gwa

A few important points:

• saltou is stressed on the last syllable
• à is a separate syllable here
• água is stressed on á
• in natural speech, the phrase may flow together smoothly

European Portuguese often reduces unstressed vowels, so native pronunciation may sound more compact than you expect from spelling.

Saltar is a very common and normal verb for to jump.

Depending on context, you may also see:

• pular in Brazilian Portuguese, very common there
• saltar is especially standard and common in European Portuguese

So for Portugal Portuguese, saltar is an excellent verb to learn.

Yes, it fits European Portuguese very well.

Two things help give that impression:

• saltar is especially natural in Portugal
• saltar à água is a very natural European Portuguese way to express jump into the water

A Brazilian speaker would understand it, but some wording choices might be different in Brazil depending on the situation.