La perdita sotto il lavandino non è grave, ma devo chiamare un idraulico.

Here, perdita means leak.

More literally, perdita often means loss in many contexts, but when talking about plumbing, water, gas, etc., it commonly means a leak. So La perdita sotto il lavandino means The leak under the sink.

Italian uses articles more often than English does.

So la perdita is natural because Italian usually says the leak rather than just leak when referring to a specific thing already identified in the situation.

• la = the
• perdita is a feminine singular noun

That is why you get la perdita.

Sotto means under or below.

So:

• sotto = under
• il lavandino = the sink

Together, sotto il lavandino means under the sink.

This is a very common structure in Italian: preposition + article + noun.

Yes. Sotto il lavandino and sotto al lavandino are both possible.

In many everyday contexts, both are understood as under the sink.
Very roughly:

• sotto il lavandino is a direct, simple structure
• sotto al lavandino is also common in spoken Italian

In a beginner sentence like this, sotto il lavandino is perfectly natural and standard.

In Italian, non usually goes directly before the verb to make it negative.

So:

• è grave = it is serious
• non è grave = it is not serious

That is why the sentence says non è grave.

The accent is important because è and e are different words:

• è = is
• e = and

So in this sentence, non è grave means is not serious, and the accent shows that this is the verb essere.

Because grave is an adjective that has the same form for masculine and feminine singular.

So:

• un problema grave = a serious problem
• una perdita grave = a serious leak

The adjective changes only in the plural:

• problemi gravi
• perdite gravi

So grave is correct with perdita.

Italian often leaves out subject pronouns when they are already clear from the verb form.

• devo already means I must or I have to

So devo chiamare un idraulico naturally means I need to call a plumber without needing io.

You could say io devo chiamare un idraulico, but that usually adds emphasis, as if you mean I have to call one.

Because with dovere, Italian normally uses the modal verb directly followed by an infinitive.

So:

• devo chiamare = I must call
• devi andare = you must go
• dobbiamo partire = we have to leave

No extra preposition is needed between dovere and the infinitive.

It is un idraulico because idraulico is a masculine singular noun beginning with a vowel sound, and the correct indefinite article is un.

So:

• un idraulico = a plumber

Not:

• uno idraulico
• un’idraulico

Also, the apostrophe form un’ is used with feminine nouns, for example:

• un’idraulica = a female plumber

So for the masculine noun idraulico, the correct form is un idraulico.

No. Lavandino is very common, especially for a bathroom or kitchen sink, but Italian also uses other words depending on region and context.

For example:

• lavandino = sink, washbasin
• lavello = sink, especially kitchen sink

So in everyday Italian, you may hear both sotto il lavandino and sotto il lavello, depending on what kind of sink is meant and where the speaker is from.

Yes, to some extent.

The original sentence is very natural:

• La perdita sotto il lavandino non è grave, ma devo chiamare un idraulico.

But Italian does allow some flexibility. For example, you could also say:

• La perdita non è grave, ma devo chiamare un idraulico.

That version simply leaves out sotto il lavandino.

You could also move parts around for emphasis in some contexts, but the original order is clear and standard for learners.