وقتی در بیمارستان منتظر بودم، یک پرستار به من آب داد.

وقتی means when.

It introduces the time clause:

• وقتی در بیمارستان منتظر بودم = when I was waiting in the hospital

So the sentence has two parts:

1. وقتی در بیمارستان منتظر بودم = when I was waiting in the hospital
2. یک پرستار به من آب داد = a nurse gave me water

It works much like English when at the beginning of a sentence.

Farsi usually prefers subject–object–verb order, and the verb often comes at the end of its clause.

So:

• در بیمارستان منتظر بودم literally looks like in the hospital waiting was-I
• یک پرستار به من آب داد literally looks like a nurse to me water gave

That is normal in Farsi. Even though the English translation sounds more natural as I was waiting / a nurse gave me water, in Farsi the verb commonly comes last.

منتظر means waiting or expectant, and بودم means I was.

Together, منتظر بودم literally means I was waiting.

This is a very common pattern in Farsi:

• adjective/state + form of بودن = being in that state

So:

• منتظر بودم = I was waiting
• خسته بودم = I was tired
• آماده بودم = I was ready

So here, instead of a single verb meaning exactly I waited, Farsi uses a state expression: I was in a waiting state.

Yes. منتظر often takes something or someone after it, meaning waiting for someone/something:

• منتظرِ دکتر بودم = I was waiting for the doctor
• منتظرِ جواب بودم = I was waiting for the answer

In your sentence, that part is simply left unstated:

• منتظر بودم = I was waiting

That sounds natural if the important point is just that the speaker was waiting, not what they were waiting for.

در means in / at, and بیمارستان means hospital.

So:

• در بیمارستان = in the hospital or at the hospital

In English, both may be possible depending on context. In Farsi, در is the normal preposition here.

یک پرستار means a nurse.

• یک = one / a
• پرستار = nurse

Here یک makes the noun indefinite, like English a.

You do not always have to use یک for an indefinite noun in Farsi, but it is very common when introducing a singular countable noun:

• یک پرستار = a nurse
• یک مرد = a man
• یک کتاب = a book

Without یک, پرستار could still sometimes be understood as a nurse, but یک پرستار is clearer and very natural.

به is a preposition meaning to, and من means me / I.

So:

• به من = to me

This is used with دادن (to give), because in Farsi the recipient is usually marked with به:

• به من کتاب داد = he/she gave me a book
• به او گفت = he/she told him/her
• به بچه آب داد = he/she gave water to the child

So یک پرستار به من آب داد is literally a nurse gave water to me.

آب means water, and داد is the past tense of دادن (to give) for he/she gave.

So:

• آب داد = gave water

In the full clause:

• یک پرستار به من آب داد = a nurse gave me water

The verb داد does not show gender, so it can mean he gave or she gave. In this sentence, since پرستار is being translated as a nurse, English naturally uses a nurse gave me water without needing a pronoun.

Good question. را often marks a specific direct object.

You might expect:

• آب را داد

But in this sentence, آب is not being treated as a specific, definite object like the water. It is more like some water or simply water, so leaving out را is natural.

Compare:

• به من آب داد = gave me water
• به من آبِ سرد داد = gave me cold water
• آب را به من داد = gave the water to me / gave me the water

So the absence of را helps the phrase sound more general and natural.

داد is the simple past form of دادن for third person singular:

• دادم = I gave
• دادی = you gave
• داد = he/she gave
• دادیم = we gave
• دادید = you gave
• دادند = they gave

Here it agrees with یک پرستار because that subject is third person singular:

• یک پرستار ... داد = a nurse ... gave

The two clauses describe different kinds of past actions:

• منتظر بودم = I was waiting → an ongoing background state/action
• آب داد = gave water → a completed event

So the sentence structure is similar to English:

• When I was waiting in the hospital, a nurse gave me water.

The waiting is the background situation, and the giving is the main event that happened during that time.

The comma is helpful, and it is commonly used here, but in everyday writing you may sometimes see punctuation used less strictly.

The comma separates:

• the time clause: وقتی در بیمارستان منتظر بودم
• the main clause: یک پرستار به من آب داد

So it works just like English:

• When I was waiting in the hospital, a nurse gave me water.

It makes the sentence easier to read.

Yes. Farsi is flexible enough that you can move the clauses around, especially with a time clause like this.

For example:

• یک پرستار به من آب داد وقتی در بیمارستان منتظر بودم.

This is understandable, but the original order is more natural and smoother:

• وقتی در بیمارستان منتظر بودم، یک پرستار به من آب داد.

Starting with وقتی is very common when you want to set the scene first.

It is neutral and standard Farsi.

Nothing in it is especially formal or slangy. It would fit well in:

• conversation
• writing
• storytelling
• textbook examples

A more colloquial spoken version might sound slightly different in pronunciation or rhythm, but the wording itself is standard and natural.