O regador está vazio.

O is the definite article, meaning the.

In Portuguese, it is very normal to use the article with a noun in a simple sentence like this:

• O regador está vazio.

Leaving it out would usually sound less natural here unless you were speaking in a special context, such as labels, headlines, or very telegraphic speech.

Also, regador is a masculine singular noun, so the article must be o:

• o regador
• not a regador

You usually have to learn the gender together with the noun: o regador.

The ending -dor is often masculine in Portuguese, especially for nouns based on actions or tools:

• o computador
• o secador
• o aspirador
• o regador

That said, gender is not always fully predictable, so it is best to memorize nouns with their article.

Portuguese has two common verbs for to be: ser and estar.

Here, está is used because empty is understood as a current condition or state, not a permanent characteristic.

So:

• O regador está vazio. = the watering can is empty right now.

This is a very common use of estar:

• A porta está aberta.
• O copo está cheio.
• A garrafa está vazia.

Using é here would sound wrong in normal Portuguese.

Está is the 3rd person singular of estar in the present tense.

The subject is o regador, which is it in English, so Portuguese uses the 3rd person singular:

• eu estou
• tu estás
• ele/ela/você está

So:

• O regador está vazio.

Adjectives in Portuguese usually agree with the noun in gender and number.

Since regador is masculine singular, the adjective must also be masculine singular:

• o regador vazio

Here are the main forms:

• vazio = masculine singular
• vazia = feminine singular
• vazios = masculine plural
• vazias = feminine plural

Examples:

• O regador está vazio.
• A garrafa está vazia.
• Os copos estão vazios.
• As caixas estão vazias.

The normal, neutral word order is:

• O regador está vazio.

That is:

• subject + verb + adjective

You can change the order in some contexts, but it usually sounds more marked, literary, or contrastive. For a learner, the safest pattern is the standard one above.

So yes, Portuguese can be flexible sometimes, but this sentence in its normal form is best learned as:

• O regador está vazio.

A careful European Portuguese pronunciation is roughly:

• /u ʁə.ɡɐˈðoɾ ɨʃˈta vɐˈziu/

A few useful pronunciation notes:

• O often sounds close to u in European Portuguese.
• The g in regador is a hard g, like in go.
• The d in regador is pronounced like a normal d sound between vowels, not like English j.
• está is stressed on the second syllable: es-TÁ.
• z in vazio sounds like z in zero.
• io at the end of vazio forms two syllables: va-ZI-o.

A rough English-friendly guide could be:

• u reh-guh-DOR esh-TA vah-ZEE-oo

But the real European Portuguese pronunciation is more reduced and less fully pronounced than English.

In everyday learning contexts, regador usually means watering can.

Because it comes from the verb regar (to water), it refers to something used for watering. In some contexts, related meanings may appear, but for most learners the important basic meaning is the common household/garden object.

So in this sentence, the learner should understand it as the ordinary noun regador used with its normal article and adjective agreement.

Yes. It is a completely natural sentence.

It follows a very common pattern in Portuguese:

• O/A + noun + está + adjective

For example:

• O copo está vazio.
• A garrafa está cheia.
• A porta está fechada.

So O regador está vazio. is a normal, idiomatic sentence in European Portuguese.