Eu vou abrir a torneira para lavar as mãos.

Yes, you usually can.

In Portuguese, subject pronouns are often omitted because the verb form already shows who the subject is. Vou clearly means I am going / I will.

So both are natural:

• Eu vou abrir a torneira para lavar as mãos.
• Vou abrir a torneira para lavar as mãos.

Using eu can add emphasis, contrast, or clarity:

• Eu vou abrir a torneira, não você.
  I’m going to open the faucet, not you.

In everyday Brazilian Portuguese, dropping eu is very common.

Vou abrir is the very common everyday way to talk about the future in Brazilian Portuguese.

It uses:

• ir in the present tense: vou
• plus an infinitive: abrir

So vou abrir literally looks like I am going to open, but in practice it often just means I will open.

The simple future abrirei is grammatical, but it sounds more formal, literary, or less conversational in Brazil. In normal speech, Brazilians usually prefer vou abrir.

Compare:

• Vou abrir a torneira. — very natural in speech
• Abrirei a torneira. — correct, but more formal

Yes. Portuguese normally says abrir a torneira and fechar a torneira.

So the faucet is thought of as something you open and close:

• abrir a torneira = turn on the tap / open the faucet
• fechar a torneira = turn off the tap / close the faucet

This is completely natural in Brazilian Portuguese.

Portuguese uses definite articles much more often than English.

So where English might say something like turn on the faucet, Portuguese naturally says abrir a torneira. The article a is normal here.

In many everyday situations, Portuguese prefers:

• a torneira
• a porta
• o carro
• a mão

rather than leaving the noun bare.

It shows purpose.

para + infinitive often means:

• to ...
• in order to ...
• for the purpose of ...

So:

• para lavar as mãos = to wash (my) hands / in order to wash (my) hands

The verb lavar stays in the infinitive because it follows para.

Other examples:

• Vou ao mercado para comprar pão.
  I’m going to the market to buy bread.
• Abri a janela para entrar ar.
  I opened the window to let air in.

This is very common with body parts in Portuguese.

When it is already obvious whose body part is being talked about, Portuguese often uses the definite article instead of a possessive:

• lavar as mãos = wash one’s hands / wash my hands
• machuquei o braço = I hurt my arm
• escove os dentes = brush your teeth

So lavar as mãos sounds natural and idiomatic.

You can say minhas mãos, but it is usually more emphatic, contrastive, or specific:

• Preciso lavar minhas mãos, não as luvas.
• Minhas mãos estão sujas.

In this sentence, as mãos is the most natural choice.

It is plural because people usually wash both hands.

• lavar as mãos = wash the hands / wash one’s hands

If you mean only one hand, you can use the singular:

• Vou lavar a mão.
  I’m going to wash my hand.

Also, mão has an irregular plural:

• mão → mãos

That is a very important word pair to memorize.

In Brazilian Portuguese, lavar as mãos is already the normal way to say wash my hands / wash your hands / wash one’s hands, depending on context.

So this is natural:

• Vou lavar as mãos.

But this is not the usual everyday phrasing:

• Vou me lavar as mãos. ❌

That sounds unnatural in Brazilian Portuguese.

A reflexive can appear in other structures, but not like that. For example:

• Vou me lavar. = I’m going to wash myself.

That means washing yourself in general, not specifically your hands.

So for this sentence, lavar as mãos is exactly the right expression.

Yes. In spoken Brazilian Portuguese, pra is extremely common.

So these both work:

• Eu vou abrir a torneira para lavar as mãos.
• Eu vou abrir a torneira pra lavar as mãos.

The difference is mainly register:

• para = more neutral, careful, or written
• pra = more informal and very common in speech

In conversation, many Brazilians would naturally say pra.

A rough Brazilian pronunciation guide:

• Eu ≈ eh-oo said quickly
• vou ≈ voh / voo with a closed o
• abrir ≈ ah-BREER
• torneira ≈ tor-NAY-ra
  The stress is on nei
• para ≈ PA-ra
• lavar ≈ la-VAR
• as mãos ≈ az MOW̃S

The hardest part for many English speakers is mãos because of the nasal sound ão. It is not a normal English vowel. You should let the sound resonate through the nose slightly.

Also, in connected speech, as mãos often sounds more like:

• az mãos

because the s in as is commonly pronounced like z before a vowel or voiced sound in fluent speech, depending on accent and context.

Yes. That is grammatical.

The original order is the most straightforward:

• Eu vou abrir a torneira para lavar as mãos.

But you can move the purpose phrase to the front:

• Para lavar as mãos, eu vou abrir a torneira.

That version gives more emphasis to the purpose.

In everyday speech, though, the original order is more neutral and common.