Перед тем как варить рис, его нужно промыть водой.

Перед тем как is a very common way to introduce a subordinate clause meaning before doing something / before something happens.

So:

• Перед тем как варить рис = before cooking rice

Russian often uses this multi-word conjunction when the before phrase contains a verb. It is best learned as a set expression.

A close alternative is прежде чем:

• Прежде чем варить рис, его нужно промыть водой.

Both are natural, though перед тем как sounds a bit more neutral and transparent to learners.

Тем is the instrumental singular form of тот (that).

It appears because of the preposition перед, which takes the instrumental in this expression:

• перед
  • тем
    • как

Historically/literally, the phrase is something like before that, how/when..., but in modern Russian you should mainly treat перед тем как as a fixed conjunction meaning before.

In this sentence, перед тем как is being treated as a single conjunction, so there is no comma inside it:

• Перед тем как варить рис, ...

This is very common.

You may also see:

• Перед тем, как варить рис, ...

That version splits the conjunction and puts a comma before как. Both can be found, but the version without the internal comma is very natural here.

The comma that must be there is the one separating the subordinate clause from the main clause:

• Перед тем как варить рис, его нужно промыть водой.

It is accusative here, but for an inanimate masculine singular noun, the accusative looks exactly like the nominative.

So:

• nominative: рис
• accusative: рис

In варить рис, рис is the direct object of варить, so it is accusative, even though the form does not change.

Варить is imperfective, and here it refers to the action of cooking rice in a general/process sense:

• перед тем как варить рис = before cooking rice

Russian often uses the imperfective after expressions like this when it refers to the activity itself, not the completed result.

Compare:

• варить рис = to cook rice, to be cooking rice
• сварить рис = to cook rice completely, to finish cooking it

You could hear перед тем как сварить рис in some contexts, but варить is very natural in general instructions.

Его refers back to рис and avoids repeating the noun:

• Перед тем как варить рис, его нужно промыть водой.

This is very natural Russian.

You could also say:

• Перед тем как варить рис, рис нужно промыть водой.

But that sounds more repetitive.

Here его is the direct object of промыть. It means it, referring to rice.

Here его is the accusative form of the pronoun meaning him/it, but in this sentence it means it because it refers to рис.

A useful thing to know is that его has the same written form in more than one case, so you identify its role from the sentence.

Here:

• его нужно промыть = it needs to be rinsed

So его is the object of промыть.

This is a very common impersonal construction in Russian.

• нужно = it is necessary / one should / you need to

So:

• его нужно промыть literally = it is necessary to rinse it
• natural English = it should be rinsed or you need to rinse it

Russian often leaves the doer unspecified in instructions, recipes, and general advice. English does something similar with you should... or passive phrasing.

Промыть is perfective because it describes a single completed action that should be done before cooking.

• промыть рис = to rinse the rice
• the idea is: do this first, and finish doing it

If you used the imperfective промывать, it would sound more like a repeated/habitual process or would focus on the action as ongoing, which is not what this instruction is aiming at.

So the aspect contrast is very natural:

• варить = the general cooking process
• промыть = the completed preparatory step

Промыть is especially natural for rinsing food with water.

Roughly:

• мыть = to wash
• помыть = to wash something
• промыть = to rinse / wash through thoroughly

For rice, промыть рис is the usual choice, because you are not really cleaning the rice like you wash a dish; you are rinsing it.

So промыть is the most idiomatic verb here.

Because the instrumental case is often used for the means or substance used to do something.

• промыть водой = rinse with water

So водой answers the idea of with what?

Compare:

• резать ножом = cut with a knife
• писать ручкой = write with a pen
• промыть водой = rinse with water

Yes. Russian word order is flexible.

For example:

• Его нужно промыть водой перед тем как варить рис.
• Перед варкой риса его нужно промыть водой.

But the original:

• Перед тем как варить рис, его нужно промыть водой.

is very natural because it starts with the time condition before cooking rice and then gives the instruction.

That order works especially well in recipes and practical instructions.

Yes. Russian often has a more compact noun-based version:

• Перед варкой риса его нужно промыть водой.

This literally means:

• Before the cooking of rice, it should be rinsed with water.

Here:

• варкой is from варка (cooking, boiling)
• риса is genitive after перед

Both versions are correct, but the original with перед тем как варить рис may feel a bit more conversational and transparent for learners.