Ja sada pijem vodu.

You can absolutely say Sada pijem vodu or even just Pijem vodu.

In Serbian, the subject pronoun is often omitted because the verb ending already tells you who is doing the action.
Here, pijem means I drink / I am drinking, so ja is not required.

Using ja adds emphasis, for example:

• Ja sada pijem vodu. = I am drinking water now.
• On sada pije vodu. = He is drinking water now.

So ja is correct, but often optional.

Sada means now.

It is not grammatically necessary, but it changes the meaning slightly by making the time explicit. Compare:

• Pijem vodu. = I drink water / I am drinking water.
• Sada pijem vodu. = I am drinking water now.

So sada helps show that this is happening at the present moment.

Yes, but only in style and register.

• sada is the full form
• sad is a very common shorter spoken form

Both mean now. In everyday speech, many speakers say sad:

• Ja sad pijem vodu.

That is completely natural. Sada may sound a bit more neutral or slightly more formal, depending on context.

Because piti is the infinitive, and pijem is the 1st person singular present tense form.

The verb changes depending on the subject. For piti (to drink), the present tense is:

• ja pijem = I drink / I am drinking
• ti piješ = you drink
• on/ona/ono pije = he/she/it drinks
• mi pijemo = we drink
• vi pijete = you drink (plural/formal)
• oni/one/ona piju = they drink

So pijem is the correct form for ja.

Because vodu is in the accusative case.

In this sentence, water is the direct object — it is the thing being drunk — so Serbian uses the accusative.

The dictionary form is:

• voda = water

But as a direct object, it becomes:

• vodu

This is a very common pattern for feminine nouns ending in -a:

• žena → ženu
• kafa → kafu
• voda → vodu

So pijem vodu literally uses the form required after the verb because water is what you are drinking.

Because Serbian does not have articles like English a and the.

So vodu can mean:

• water
• the water
• sometimes even some water

The exact meaning depends on context.

That is normal in Serbian. Learners often look for an article, but there simply is none.

It is present tense, and it can mean both depending on context.

• Pijem vodu. can mean I drink water in a general sense.
• It can also mean I am drinking water right now.

When you add sada, the meaning is much more clearly:

• Ja sada pijem vodu. = I am drinking water now.

So the Serbian present tense often covers both English simple present and present continuous.

The word order is flexible.

Ja sada pijem vodu is perfectly correct, but Serbian allows other orders too, depending on emphasis:

• Sada pijem vodu.
• Pijem vodu sada.
• Vodu sada pijem.
• Ja pijem vodu sada.

The most neutral versions are usually:

• Sada pijem vodu
• Ja sada pijem vodu
• Pijem vodu

If you move words around, you often change what is being emphasized rather than the basic meaning.

Yes. That is a very natural sentence.

It means:

• I am drinking water
• or I drink water

depending on context.

You only add ja if you want emphasis, and you only add sada if you want to stress now.

So:

• Pijem vodu. = natural and common
• Ja pijem vodu. = emphasizes I
• Sada pijem vodu. = emphasizes now
• Ja sada pijem vodu. = emphasizes both

A rough pronunciation guide is:

• Ja ≈ yah
• sada ≈ SAH-dah
• pijem ≈ PEE-yem
• vodu ≈ VOH-doo

A fuller approximation:

yah SAH-dah PEE-yem VOH-doo

A few helpful notes:

• j in Serbian is pronounced like English y in yes
• v is a clear v
• d and t are usually clean and crisp
• stress is not marked in normal writing, so learners usually pick it up through listening

Yes, but the form depends on the noun.

For example:

• Ja sada pijem kafu. = I am drinking coffee now.
• Ja sada pijem sok. = I am drinking juice now.
• Ja sada pijem mleko. = I am drinking milk now.

Notice:

• kafa → kafu in the accusative
• sok stays sok
• mleko stays mleko

So the case pattern depends on the gender and noun type, but the basic sentence structure stays the same.

Yes, it is grammatically correct and natural.

That said, in everyday conversation, many speakers would probably choose a slightly shorter version unless emphasis is needed:

• Sad pijem vodu.
• Pijem vodu.

So Ja sada pijem vodu is fine, but it may sound a bit more explicit than necessary in casual speech unless you are stressing I or now.