После падения нужно промыть рану водой.

Because после always takes the genitive case.

The basic form is падение (a fall), but after после it becomes падения.

• nominative: падение
• genitive: падения

So:

• после падения = after a fall / after falling

This is a very common pattern:

• после урока = after the lesson
• после дождя = after the rain
• после аварии = after the accident

Падения is the genitive singular of падение.

Падение is a neuter noun meaning fall or falling. In this sentence, it refers to the event of falling.

So grammatically:

• dictionary form: падение
• form used here: падения
• reason: it follows после, which requires the genitive

A learner might expect something more like a verb form, but Russian often uses nouns like this where English might use after falling.

Нужно is an impersonal word meaning it is necessary, it is needed, or more naturally in English, you need to / one should.

In this sentence, there is no specific subject stated. Russian often uses this kind of impersonal construction for instructions, advice, and general rules.

So:

• нужно промыть рану водой = it is necessary to rinse the wound with water
• more natural English: you need to rinse the wound with water

This is very common in medical advice, instructions, and signs.

Compare:

• Нужно подождать. = You need to wait.
• Нужно позвонить врачу. = You need to call a doctor.

Yes, in a sense—but it is not grammatically stated.

Russian often leaves the subject unstated in general instructions. Here, the meaning is something like:

• one should rinse the wound with water
• you should rinse the wound with water

So the sentence is impersonal. It does not mean that some specific person is named or implied grammatically; it is just a general recommendation.

If you wanted to make the person more explicit, you could say things like:

• Вам нужно промыть рану водой. = You need to rinse the wound with water.

But in general advice, Russian often simply says нужно + infinitive.

Промыть is a perfective verb, while мыть is generally imperfective.

Here, perfective makes sense because the sentence talks about a single complete action:

• промыть = to rinse out / wash thoroughly / wash once as a completed action

In instructions, Russian often prefers the perfective infinitive when the goal is to tell someone to do a complete action.

Compare:

• мыть = to wash, to be washing, to wash habitually
• промыть = to wash through, rinse, wash out completely once

A related imperfective verb would be промывать.

So:

• нужно промыть = you need to rinse/wash it properly once
• нужно промывать could suggest repeated or ongoing washing

In промыть, the prefix про- adds the idea of washing something through, out, or thoroughly.

So мыть is just to wash, but промыть often means:

• rinse
• wash out
• clean by washing through

That is why промыть рану is a natural medical phrase: it means to clean the wound by rinsing it.

Similar examples:

• промыть глаза = rinse the eyes
• промыть нос = rinse the nose
• промыть рану = rinse the wound

Because рану is the accusative singular form of рана.

Рана is a feminine noun, and here it is the direct object of the verb промыть.

• nominative: рана = a wound
• accusative: рану = a wound (as the object)

So:

• промыть рану = to rinse the wound

This is a standard pattern for feminine nouns ending in -а:

• книга → читать книгу
• машина → мыть машину
• рана → промыть рану

Because водой is the instrumental case.

Russian often uses the instrumental to show the means or substance used to do something. Here, the wound is rinsed with water, so вода becomes водой.

• nominative: вода = water
• accusative: воду
• instrumental: водой

So:

• промыть рану водой = rinse the wound with water

This instrumental usage is very common:

• писать ручкой = write with a pen
• резать ножом = cut with a knife
• лечить лекарствами = treat with medicines

Because Russian does not always need a preposition for English with.

In this sentence, водой is instrumental without a preposition, and that alone can express the idea of by means of / with.

So:

• промыть рану водой = wash the wound with water

If you used с водой, that would usually mean something more like together with water or in a different context, not the normal way to express the means here.

This is a useful thing to remember: English often uses a preposition where Russian simply uses a case ending.

Yes. Russian word order is fairly flexible because the case endings already show the grammatical roles.

The neutral order here is:

• После падения нужно промыть рану водой.

But other orders are possible, depending on emphasis:

• Рану после падения нужно промыть водой.
• После падения рану нужно промыть водой.

These all mean roughly the same thing, but the focus shifts a little.

The original version sounds natural and neutral, especially in instructional language.

Yes. Russian has several ways to express after falling or after a fall, but после падения is very natural and compact.

Other possibilities include:

• если вы упали, нужно промыть рану водой = if you have fallen, you need to rinse the wound with water
• после того, как вы упали, ... = after you fell, ...

However, после падения is the most concise and instruction-like version. It sounds exactly like the kind of wording you would find in first-aid guidance.

Yes. In many contexts, нужно and надо are very close in meaning.

So you could also say:

• После падения надо промыть рану водой.

Both are natural. Very roughly:

• нужно can sound a little more neutral or formal
• надо can sound a little more conversational

But in practice, both work well here.

It is most naturally read as a general instruction or practical advice.

Because of нужно + infinitive, it sounds like:

• what should be done
• the proper procedure
• recommended action

It is not as strong as a strict command in the imperative, such as:

• Промойте рану водой. = Rinse the wound with water.

So the original sentence is slightly less direct and more instructional in tone.