Learn Hardcore Portuguese (Portugal): A empregada de mesa traz água para o jantar.

A empregada de mesa = The waitress (a specific one we have in mind)
Empregada de mesa traz água… – without the article – sounds like a headline, a note, or very telegraphic language, not a normal full sentence.

Portuguese uses definite articles more than English. Whenever you say the X as a normal subject in English, you should expect o/a X in Portuguese:

A criança chora. – The child is crying.
O carro está na rua. – The car is in the street.

What exactly does empregada de mesa mean? Is it the usual word for waitress in Portugal?

Literally, empregada de mesa means table employee.

empregada = female employee / worker
de mesa = of the table (i.e. the person who serves at the tables)

In Portugal, empregada de mesa (feminine) and empregado de mesa (masculine) are standard, neutral ways to say waitress and waiter, especially in more formal / written contexts and in job descriptions.

In everyday spoken Portuguese in a restaurant, people might also say:

empregada / empregado (when the context already makes it clear it’s restaurant staff)
funcionária de mesa / funcionário de mesa (also possible, a bit more “corporate” sounding)

Terms like garçonete are mainly Brazilian; in Portugal they sound foreign or at least non-standard.

Why is it empregada (with -a) here? What would the masculine version be?

Portuguese nouns referring to people usually show grammatical gender:

empregada = female employee
empregado = male employee

So:

A empregada de mesa traz água… – The waitress brings water…
O empregado de mesa traz água… – The waiter brings water…

In job ads or neutral references you might see empregado(a) de mesa to include both genders in writing.

What is traz? How is it related to trazer?

Trazer is the infinitive to bring.

Traz is the present tense, 3rd person singular (ele/ela/você):

eu trago – I bring
tu trazes – you bring (informal singular)
ele / ela / você traz – he / she / you bring
nós trazemos – we bring
vocês / eles / elas trazem – you (pl.) / they bring

Since the subject is A empregada de mesa (she), you use traz:

A empregada de mesa traz água… – The waitress brings (is bringing) water…

Can traz mean both brings and is bringing?

Yes. In Portuguese, the simple present often covers both English present simple and present continuous.

So A empregada de mesa traz água para o jantar can mean:

The waitress brings water for dinner (habitual, general fact)
The waitress is bringing water for dinner (right now / in this situation)

Context does the work.

If you really want to highlight the ongoing nature of the action (especially in European Portuguese), you can say:

A empregada de mesa está a trazer água para o jantar. – The waitress is bringing water for dinner (right now).

(Brazilian Portuguese would say está trazendo instead of está a trazer.)

Why is it traz água and not traz a água?

Portuguese often omits the article with mass nouns (like água) when you mean some water / water in general, not a specific, identifiable water.

traz água – brings (some) water in general
traz a água – brings the water (the particular water we already know or have mentioned: for example, the bottle we ordered, or the jug on the counter)

So:

A empregada de mesa traz água para o jantar.
→ She brings water for dinner (a normal, expected part of the meal).
A empregada de mesa traz a água que pedimos.
→ She brings the water that we ordered (a specific item previously identified).

What does para o jantar express here? Could we also say para jantar?

Para o jantar here means for the dinner (meal) – the water is intended for that dinner.

para o jantar – for the dinner (as an event / meal)
para jantar – for dinner / to have dinner (more about the activity or purpose than a specific meal event)

Both can be correct, but the nuance shifts slightly:

Comprei vinho para o jantar.
I bought wine for the dinner (this specific dinner we are talking about).
Comprei vinho para jantar.
I bought wine to have with dinner / so that we can have dinner (with wine) – more about purpose/activity.

In your sentence, para o jantar sounds very natural because we’re talking about the water that is going to be on the table with the dinner.

Why is para used here and not por or a for for dinner?

Para is the usual preposition for destination, purpose, or intended recipient.

In água para o jantar, para shows purpose:

water for dinner (its purpose is to accompany the dinner)

Roughly:

para ≈ for the purpose of / to / in order to / to someone
por ≈ because of / through / by / per

So:

Comprei flores para o jantar. – I bought flowers for the dinner (to use at that dinner).
Comprei flores por causa do jantar. – I bought flowers because of the dinner.

Using por in água por o jantar would be incorrect for the meaning for dinner.

What is the o in para o jantar? Is there a contraction?

The o is the masculine singular definite article for jantar (dinner, the meal):

o jantar – the dinner
para o jantar – for the dinner

In standard writing in Portugal, you usually keep them separate: para o jantar.

In fast speech, many people pronounce it almost like one unit, something like:

[paɾu ʒɐ̃ˈtaɾ] or [pɾu ʒɐ̃ˈtaɾ]

In Brazilian Portuguese you’ll often see and hear the contraction pro:

pro jantar = para o jantar (informal spelling, common in Brazil)

In European Portuguese, you mostly write para o jantar, even if the speech is a bit contracted.

Does jantar here mean the noun dinner or the verb to have dinner?

Here, jantar is a noun: o jantar = the dinner (meal).

Portuguese has both:

o jantar – the dinner (noun)
jantar – to have dinner (verb)

Examples:

Vamos jantar às oito. – We’re going to have dinner at eight. (verb)
O jantar é às oito. – Dinner is at eight. (noun)

In água para o jantar, since it has the article o, it must be the noun: water for the dinner.

Can we change the word order, like A empregada de mesa traz para o jantar água?

Portuguese word order is relatively flexible, but there is a default order:

Subject – Verb – Direct object – Other complements
A empregada de mesa – traz – água – para o jantar

Your alternative:

A empregada de mesa traz para o jantar água.

This is grammatically possible, but:

It sounds slightly more marked / stylised.
It puts a bit more focus on para o jantar (for dinner) before specifying what she brings.

The most neutral and natural version is the original:

A empregada de mesa traz água para o jantar.

How should I pronounce empregada de mesa traz água para o jantar in European Portuguese?

Here is a rough European Portuguese pronunciation (not strict IPA, but close):

A empregada de mesa → ah ẽ-pɾeh-GAH-dɐ dɨ ME-zɐ
- empregada: stress on ga – ẽ-pɾeh-GAH-dɐ
- de in unstressed position is usually like dɨ, not dee.
traz → tɾaʃ
- Final -z often sounds like sh (ʃ) in European Portuguese.
água → AH-gwa
- Stress on Á; gu
  - a gives gwa.
para o → often PA-ɾu or PA-ɾɐ u in careful speech, more like one group in fast speech.
jantar → ʒɐ̃-TAɾ
- Initial j = zh sound as in measure.
- an is nasal: ɐ̃.
- Stress on tar.

Spoken naturally, it runs together roughly as: > Ah ẽpɾeGA-dɐ dɨ ME-zɐ tɾaʃ AH-gwa paɾu ʒɐ̃TAɾ.