Μετά το χτεσινό ξενύχτι, πίνω μόνο νερό σήμερα.

Μετά means after.

In this sentence, μετά is followed by a noun phrase in the accusative:

• μετά το χτεσινό ξενύχτι = after last night’s staying up late / after last night’s all-nighter

So the structure is:

• μετά + accusative noun phrase = after ...

Examples:

• μετά το φαγητό = after the meal
• μετά τη δουλειά = after work
• μετά το μάθημα = after class

Here, the whole opening phrase gives the context for the rest of the sentence.

Ξενύχτι is a noun that refers to staying up very late, often all night, or the resulting sleepless night / late night.

It comes from the idea of being awake through the night. Depending on context, it can suggest:

• a night out
• not getting enough sleep
• an all-nighter
• staying up too late

So το χτεσινό ξενύχτι is something like:

• last night’s staying up late
• last night’s all-nighter
• the late night I had yesterday

It is a very natural Greek word and is commonly used in everyday speech.

Χτεσινό is the form that agrees with ξενύχτι.

The adjective is basically χτεσινός / χτεσινή / χτεσινό, meaning yesterday’s or from yesterday / last night’s, depending on context.

Because ξενύχτι is:

• neuter
• singular

the adjective also has to be:

• neuter singular → χτεσινό

So:

• ο χτεσινός καφές = yesterday’s coffee
• η χτεσινή βραδιά = last night / yesterday evening
• το χτεσινό ξενύχτι = last night’s staying up late

This is normal adjective agreement in Greek.

Yes, they refer to the same word.

You may see both:

• χτεσινός
• χθεσινός

In everyday modern speech, forms with χτε- are very common. The version with χθε- is more conservative in spelling and may look a bit more formal or traditional.

A learner should recognize both. In actual pronunciation, people usually say something close to χτε-.

Greek often leaves out subject pronouns when they are not needed.

The verb ending already shows the subject:

• πίνω = I drink / I am drinking

So Greek normally says:

• πίνω νερό = I drink water / I’m drinking water

instead of:

• εγώ πίνω νερό

You can add εγώ if you want emphasis, contrast, or clarity:

• Εγώ πίνω μόνο νερό σήμερα. = I’m only drinking water today.
  This might imply not other people or not me normally, but today yes.

So leaving out I here is completely natural.

Because the sentence is not saying that the drinking happened last night. It is saying that because of last night, today the speaker drinks only water.

So the time frame is:

• μετά το χτεσινό ξενύχτι = after last night’s late night
• πίνω μόνο νερό σήμερα = today I drink / I’m drinking only water

Greek present tense here works like English I drink or I’m drinking, depending on context.

So πίνω can mean:

• I drink
• I am drinking

In this sentence, with σήμερα, it naturally means something like:

• I’m only drinking water today or
• I only drink water today

The first is usually the more natural English translation.

Μόνο means only, and here it modifies νερό.

So:

• πίνω μόνο νερό = I drink only water

This means the thing being limited is water: water and nothing else.

Greek word order is fairly flexible, but this placement is the most straightforward and natural.

Compare:

• πίνω μόνο νερό = I drink only water
• μόνο νερό πίνω = It’s only water that I drink / I only drink water
  This sounds more emphatic.

So the sentence uses the neutral, everyday order.

Because in Greek, just like in English, you often do not use the article when talking about a substance in a general way.

So:

• πίνω νερό = I drink water

not necessarily:

• πίνω το νερό

If you said το νερό, it would usually refer to some specific water:

• the water on the table
• the water you gave me
• the water in the glass

But here the meaning is general: the speaker is choosing water as their only drink. So μόνο νερό is exactly what you would expect.

It is the accusative singular, because it is the direct object of πίνω.

• πίνω τι; → νερό

However, with many neuter nouns in Greek, the nominative and accusative look the same. So νερό looks identical in both cases.

That is why you do not see a special ending change here.

Greek word order is flexible, and σήμερα can appear in different places.

The sentence:

• Μετά το χτεσινό ξενύχτι, πίνω μόνο νερό σήμερα.

is natural and clear. Putting σήμερα at the end gives it a slight “for today” feel.

You could also hear:

• Σήμερα πίνω μόνο νερό.
• Μετά το χτεσινό ξενύχτι, σήμερα πίνω μόνο νερό.

All are possible, but they shift emphasis a little.

Very roughly:

• Σήμερα πίνω μόνο νερό = emphasis on today
• πίνω μόνο νερό σήμερα = the sentence builds toward today
• Μετά το χτεσινό ξενύχτι... = first give the reason/background

The comma separates the introductory phrase from the main clause.

• Μετά το χτεσινό ξενύχτι, = background/context
• πίνω μόνο νερό σήμερα. = main statement

This is similar to English:

• After last night’s all-nighter, I’m only drinking water today.

The comma helps readability and is perfectly natural.

Yes, but μετά is the most direct and natural choice for after.

For example, Greek might sometimes use other structures depending on nuance, but in this sentence:

• Μετά το χτεσινό ξενύχτι...

is simple, idiomatic, and exactly what a native speaker would say.

So as a learner, this is a very good model to remember:

• Μετά + accusative = after something

It is basically neutral everyday Greek.

Nothing in it is especially formal. Words like πίνω, νερό, σήμερα, and μετά are completely standard.
Ξενύχτι is also very common in normal speech.

So this sentence sounds natural in conversation.

It can do either, because the Greek present tense often covers both:

• right now / around now
• a current temporary habit
• a general habit

With σήμερα, the most natural interpretation is temporary and current:

• Today I’m only drinking water

So it does not necessarily mean the speaker is drinking water at this exact second. It can mean that, for the whole day, water is the only drink they’re choosing.

Greek can move words around for emphasis.

For example:

• Μετά το χτεσινό ξενύχτι, μόνο νερό πίνω σήμερα.
• Σήμερα, μετά το χτεσινό ξενύχτι, πίνω μόνο νερό.
• Εγώ σήμερα πίνω μόνο νερό.

These all mean roughly the same thing, but the focus changes a bit.

The original version is a very balanced, natural sentence:

• context first
• then the action
• then the time word

So it is a good standard model for learners.