Пока вода кипит, я читаю книгу.

Here пока means while.

So Пока вода кипит, я читаю книгу means While the water is boiling, I read / am reading a book.

A useful thing to know is that пока has several meanings in Russian depending on context:

• while / as long as
• for now / so far
• bye in informal speech

In this sentence, it is a conjunction introducing a time clause: while the water boils/is boiling.

Because Пока вода кипит is a subordinate clause, and Russian normally separates subordinate clauses from the main clause with a comma.

So the structure is:

• Пока вода кипит = subordinate clause
• я читаю книгу = main clause

That is why you write:

Пока вода кипит, я читаю книгу.

If you reverse the order, the comma is still needed:

Я читаю книгу, пока вода кипит.

Because вода is the subject of the verb кипит, so it is in the nominative case.

Here:

• вода = the water
• кипит = boils / is boiling

Since the water is the thing doing the action, nominative is the normal form.

The infinitive is кипеть = to boil.

Its present-tense forms are:

• я киплю (rare in ordinary use for water; more often about emotion or activity)
• ты кипишь
• он/она/оно кипит
• мы кипим
• вы кипите
• они кипят

So вода кипит is simply the correct 3rd person singular present tense form.

For water, кипит often means both:

• boils
• is boiling

Russian present tense often covers both simple present and present progressive meanings.

Читаю is the 1st person singular present tense of читать = to read.

So:

• я читаю = I read / I am reading

It matches я, the subject.

The full idea is that while one action is happening (the water is boiling), another action is going on at the same time (I am reading a book).

Because читать is imperfective, and imperfective is normally used for:

• ongoing actions
• repeated actions
• background actions
• simultaneous actions

That fits this sentence perfectly: you are describing an activity in progress while something else is happening.

Прочитать is the perfective partner and means something like to read through / finish reading.
Its form прочитаю is actually future, not present:

• я прочитаю книгу = I will read / finish reading the book

So in this sentence, читаю is the natural choice because the action is presented as ongoing, not completed.

Because книгу is the accusative singular form of книга.

Книга is the direct object of читать:

• читать что? — книгу

For many feminine nouns ending in -а, the accusative singular changes to -у:

• книга → книгу
• газета → газету
• машина → машину

So:

• я читаю книга ❌
• я читаю книгу ✅

Russian often can omit subject pronouns when the verb form already makes the subject clear.

So both are possible:

• Пока вода кипит, я читаю книгу.
• Пока вода кипит, читаю книгу.

Both can mean the same thing.

Including я can make the sentence:

• slightly clearer
• slightly more explicit
• a little more natural in some contexts, especially for learners

So я is not always required, but it is completely normal here.

Yes. Russian word order is fairly flexible.

You can also say:

• Я читаю книгу, пока вода кипит.

This has basically the same meaning: I read/am reading a book while the water is boiling.

The difference is mainly one of focus:

• Пока вода кипит, я читаю книгу.
  Starts with the time/background situation.
• Я читаю книгу, пока вода кипит.
  Starts with what I am doing.

Both are natural.

It can mean either, depending on context.

Russian present tense is often broader than English. So this sentence could mean:

• Right now: While the water is boiling, I’m reading a book.
• Habitually / generally: While the water boils, I read a book.

In real life, context usually tells you which meaning is intended.

Because Russian does not have a separate tense like the English present progressive.

English distinguishes:

• I read
• I am reading

Russian usually uses the same present-tense form for both:

• я читаю

Likewise:

• вода кипит can mean the water boils or the water is boiling

Instead of a special progressive form, Russian relies on:

• context
• aspect
• time expressions
• the overall situation

Not always.

In this sentence, yes: while.

But пока can also mean:

• for now / so far
  Пока всё хорошо. = So far everything is fine.
• bye
  Пока! = Bye!

So learners have to identify its meaning from context. Here, because it introduces a clause with a verb, it clearly means while.

Yes, in some contexts пока can be close to as long as. But in this sentence, while is the most natural translation.

Why?

Because the sentence mainly describes two actions happening at the same time:

• the water is boiling
• I am reading

As long as can sound more like a condition or duration limit in English, while while sounds more straightforward here.

The stressed syllables are:

• пока́
• вода́
• кипи́т
• я
• чита́ю
• кни́гу

So a rough pronunciation guide is:

• pah-KA
• vah-DA
• kee-PEET
• ya
• chee-TA-yu
• KNEE-goo

Stress matters a lot in Russian, so it is worth learning words together with their stress.

Because Russian has no articles.

So Russian does not have separate words corresponding exactly to a and the.

That means:

• вода can mean water or the water
• книгу can mean a book or the book

Which one sounds best in English depends on context.

In this sentence, English might naturally say:

• While the water is boiling, I’m reading a book.

But Russian does not mark that difference with articles.

It describes the process.

Кипеть / кипит means to boil / be boiling, focusing on the ongoing state or activity.

If you wanted to talk about the moment when the water comes to a boil, Russian often uses a different verb, such as закипеть:

• Вода закипела. = The water started boiling / came to a boil.

So in your sentence, вода кипит means the boiling is already happening, and during that time, you are reading.

The pattern is:

Пока + subject + verb, subject + verb + object

More specifically:

• Пока вода кипит
  = While the water is boiling
• я читаю книгу
  = I am reading a book

This is a very common Russian pattern for showing simultaneous actions.

You can build many similar sentences:

• Пока мама готовит, я делаю уроки.
  While Mom is cooking, I do/am doing homework.
• Пока он работает, она слушает музыку.
  While he is working, she listens/is listening to music.