Официант разливает воду по стаканам.

Because it is the direct object of the verb разливает.

The dictionary form is вода. In this sentence, it changes to the accusative case:

• nominative: вода
• accusative: воду

A useful pattern:

• кто? что? → subject form: вода
• кого? что? → direct object form: воду

So Официант разливает воду means the waiter is pouring water.

Стаканам is in the dative plural.

After по, Russian often uses the dative when the meaning is something like throughout, over, among, or into separate containers/places.

Here, разливать что-то по стаканам means to pour something into glasses, distributing it among the glasses.

The noun changes like this:

• dictionary form: стакан = glass
• plural: стаканы
• dative plural: стаканам

So:

• по стаканам = into the glasses / among the glasses

This construction emphasizes distribution into multiple glasses, not just one.

This is a very common question, because both can relate to pouring.

• наливать usually means to pour (into a container), often focusing on filling one cup, glass, bowl, etc.
• разливать usually means to pour out / distribute into several containers.

So:

• Официант наливает воду в стакан = The waiter is pouring water into a glass.
• Официант разливает воду по стаканам = The waiter is pouring water into the glasses, distributing it among them.

In your sentence, разливает is natural because the water is being divided among multiple glasses.

Разливает is the imperfective form. Russian uses the imperfective when focusing on:

• the process
• an action in progress
• a habitual action
• a general description of what someone does

So this sentence sounds like:

• the waiter is pouring water into the glasses
• or the waiter pours water into the glasses (as a regular action, depending on context)

The perfective partner is usually разольёт / разлить, which would focus more on completion:

• Официант разольёт воду по стаканам = The waiter will pour the water into the glasses / will finish distributing it

So разливает is used because the sentence describes the action as ongoing or generally happening.

Yes, but the nuance is a little different.

• в стаканы = into the glasses
• по стаканам = among the glasses / into separate glasses, with a stronger sense of distribution

With разливать, по стаканам is especially natural because the verb itself already suggests spreading or distributing liquid.

So:

• разливать воду по стаканам sounds very idiomatic
• наливать воду в стаканы is also possible, but it feels more neutral and less focused on distribution

Russian does not have articles like English a/an and the.

So Официант can mean:

• a waiter
• the waiter

and воду can mean:

• water
• the water

You understand which one is meant from the context.

This is normal in Russian. Learners often want to know how definiteness is shown, and the answer is: usually through:

• context
• word order
• stress/intonation
• sometimes extra words like этот = this

Yes. Russian word order is more flexible than English because case endings show each word’s role.

The neutral order here is:

• Официант разливает воду по стаканам.

But other orders are possible, for example:

• Воду официант разливает по стаканам.
• По стаканам официант разливает воду.

These can change the emphasis:

• fronting воду may emphasize the water
• fronting по стаканам may emphasize where/how it is being distributed

Even though the order changes, the cases still tell you:

• официант = subject
• воду = direct object
• по стаканам = destination/distribution phrase

A helpful approximate pronunciation is:

raz-lee-VA-yet

A few details:

• раз- = raz
• ли sounds like lee
• the stress is on ва: разлива́ет
• the ending -ет here sounds like yit / yet depending on how narrowly you transcribe it

So: разлива́ет

If you want to sound more natural, make sure the stress is not on the first syllable.

Yes, официант is the masculine form.

A female waiter can be called:

• официантка

So you could say:

• Официант разливает воду по стаканам. = the male waiter is pouring water into the glasses
• Официантка разливает воду по стаканам. = the female waiter is pouring water into the glasses

Notice that in the present tense, the verb form разливает stays the same for both:

• официант разливает
• официантка разливает

Gender matters more visibly in the past tense, for example:

• Официант разливал воду
• Официантка разливала воду

The sentence follows this structure:

• Официант = subject
• разливает = verb
• воду = direct object in the accusative
• по стаканам = prepositional phrase with по
  • dative plural

So the pattern is:

[subject] + [verb] + [thing being poured] + [where it is distributed]

A useful mini-pattern to remember is:

• разливать что? по чему?

For example:

• разливать сок по чашкам = to pour juice into cups
• разливать суп по тарелкам = to ladle soup into plates/bowls
• разливать чай по кружкам = to pour tea into mugs

This sentence is a good example of how Russian uses both case endings and verb choice to express meaning very precisely.