Ahhoz, hogy ne legyen szivárgás, elzárjuk a főcsapot.

Ahhoz, hogy is a very common Hungarian structure meaning in order to, so that, or for ... to.

Literally, ahhoz means something like to that / for that, but in this pattern you should really learn ahhoz, hogy as a fixed expression.

So:

• Ahhoz, hogy ne legyen szivárgás...
  = In order for there not to be a leak...
  = So that there is no leakage...

It introduces a purpose clause: it explains why the main action is done.

Because after ahhoz, hogy in a purpose clause, Hungarian normally uses a form that corresponds to the subjunctive / imperative-type form.

Here:

• legyen = the 3rd person singular imperative/subjunctive form of van (to be)
• ne legyen = so that there won’t be / so that there may not be

Why not the others?

• nem van is not how Hungarian normally says is not. For van, the negative present is usually nincs or nincsen.
• nem lesz means will not be, which is a straightforward future statement, but here the sentence is expressing purpose, not just future time.

So:

• ne legyen szivárgás = so that there be no leakage / so that there won’t be leakage

This is very natural Hungarian.

Yes. Legyen is the imperative/subjunctive form of van (to be), and it is irregular.

Some important forms are:

• van = is
• legyen = let it be / may it be / should be

With negation:

• ne legyen = let it not be / so that there won’t be / so that there be no

This is one of those forms you simply have to memorize. It is extremely common in Hungarian.

Because szivárgás is being used in a general, non-specific sense: leakage / a leak as a phenomenon.

So:

• ne legyen szivárgás = so that there is no leakage / so that there isn’t a leak

Hungarian often leaves out the article in cases where English might or might not use one depending on style.

Compare:

• Van probléma. = There is a problem.
• Nincs idő. = There is no time.
• Ne legyen szivárgás. = Let there be no leakage / So that there is no leak.

If you added an article, it would usually make the noun more specific.

The verb elzár means to shut off, to close off, or to turn off something like a valve, tap, gas supply, or water supply.

The prefix el- often adds the sense of away/off/completely.

So:

• zár = close
• elzár = shut off, close off

In this sentence, elzárjuk a főcsapot means:

• we shut off the main valve/tap
• we turn off the main water tap

This is the natural verb for stopping the flow.

Because Hungarian verbs conjugate differently depending on whether they have a definite object.

Here the object is:

• a főcsapot = the main tap / the main valve

That is a definite object, so Hungarian uses the definite conjugation.

So:

• elzárunk = we shut off (something non-specific)
• elzárjuk = we shut it off / we shut off the specific one

Since the sentence has a főcsapot (the main tap/valve), elzárjuk is required.

Because főcsap is the direct object of the verb elzárjuk, so it takes the accusative ending -t.

• base form: főcsap = main tap / main valve
• accusative: főcsapot

So:

• elzárjuk a főcsapot = we shut off the main tap/valve

The article a stays the same here, but the noun gets the object ending.

Főcsap literally means main tap, but in natural English it is often better translated as:

• main valve
• main shutoff valve
• main water shutoff

It depends on context.

Hungarian often uses csap for things that English may call either a tap, faucet, or valve, depending on the situation. In plumbing contexts, főcsap is usually the main water shutoff.

Hungarian often puts the purpose clause first, especially when it sets up the reason for the action.

So the structure is:

• Ahhoz, hogy ne legyen szivárgás,
  elzárjuk a főcsapot.

That is basically:

• In order to avoid leakage, we shut off the main valve.

This word order is very natural because the speaker first gives the goal and then the action.

You could also say something like:

• Elzárjuk a főcsapot, hogy ne legyen szivárgás.

That would also be understandable and natural. The given version just puts stronger focus on the purpose.

Because the sentence begins with a subordinate clause:

• Ahhoz, hogy ne legyen szivárgás,

and then comes the main clause:

• elzárjuk a főcsapot

Hungarian uses a comma before the main clause in this kind of structure, just as English often does with introductory clauses.

Hungarian often uses 1st person plural in instructions, explanations, and general procedures where English might also say:

• we turn off...
• you turn off...
• one turns off...

So elzárjuk a főcsapot can mean literal we shut off the main valve, but in context it may function more like an instructional or general statement:

• we shut off the main valve
• you shut off the main valve
• the main valve is shut off

The exact English translation depends on context, but the Hungarian sentence itself is completely normal.

Yes. You can often say simply:

• Hogy ne legyen szivárgás, elzárjuk a főcsapot.

That also means:

• So that there is no leakage, we shut off the main valve.

However, ahhoz, hogy is a very common and slightly more explicit way to mark purpose. It often sounds a bit more complete or formal.

So both are possible, but ahhoz, hogy is a useful structure to learn well.

Yes, in meaning it is very close.

The Hungarian sentence literally works through a clause:

• in order that there be no leakage

But natural English often prefers:

• To prevent leakage, we shut off the main valve.
• To avoid a leak, we turn off the main tap.

So the Hungarian structure is not a direct infinitive like English to prevent, but the meaning is essentially the same.