Quan hi ha una fuita, es posa una galleda a sota fins que arriba la veïna.

In a sentence like Quan hi ha una fuita, quan introduces a general or habitual situation.

So this can mean:

• when there is a leak
• or more naturally in English, whenever there is a leak

Catalan often uses quan this way for repeated situations, just like English when can sometimes mean whenever.

Hi ha is the standard Catalan way to say there is or there are.

It comes from the verb haver-hi, which is a fixed expression. So:

• hi ha una fuita = there is a leak
• hi ha dues fuites = there are two leaks

The hi is not optional here. You normally learn haver-hi as a unit meaning to exist / there is / there are.

Fuita means leak, escape, or outflow, depending on context.

In this sentence, because there is a bucket underneath, it clearly means a leak, probably a water leak.

It is a feminine noun:

• una fuita
• la fuita

So the feminine article is completely normal here.

Here es posa is an impersonal or passive-like construction.

It is a very common Catalan pattern:

• es posa una galleda = a bucket is put down / one puts a bucket

The es removes the focus from the person doing the action. The sentence is not interested in who puts the bucket there. It is just describing what is done in that situation.

Compare:

• Posa una galleda a sota = Put a bucket underneath or He/she puts a bucket underneath, depending on context
• Es posa una galleda a sota = A bucket is put underneath / One puts a bucket underneath

It sits somewhere between the two, and English can translate it in different ways.

Possible translations include:

• a bucket is put underneath
• one puts a bucket underneath
• you put a bucket underneath in a general sense

Catalan uses es + verb very often when the doer is unknown, irrelevant, or general. English sometimes prefers a passive, and sometimes prefers a general you or they.

So grammatically, it is often described as an impersonal or pronominal passive construction.

A sota means underneath or below.

In this sentence, it stands on its own, meaning something like under it or underneath. The thing it refers to is understood from context: under the leak.

A useful contrast is:

• sota la taula = under the table
• a sota = underneath / down below

So a sota works well when no noun follows directly.

In this sentence, arriba is present indicative because the whole sentence describes a general, repeated situation.

The meaning is roughly:

• Whenever there is a leak, a bucket is put underneath until the neighbor arrives

Since this is a habitual statement, the present indicative sounds natural.

For a single future situation, Catalan often uses the subjunctive:

• Posarem una galleda a sota fins que arribi la veïna
  = We will put a bucket underneath until the neighbor arrives

So:

• arriba fits a general/habitual description
• arribi is common for a specific future event

Yes. Veïna is specifically female neighbor.

The masculine form is veí.

So:

• el veí = the male neighbor
• la veïna = the female neighbor

If the speaker says la veïna, they are referring to a woman.

Because Catalan normally uses the definite article in the same way English does here:

• la veïna = the neighbor

It refers to a specific neighbor, presumably one already known in the situation.

There is nothing unusual about the article here. It is just the ordinary feminine singular definite article.

This word order is very natural because it presents the action first and the bucket as new information.

• es posa una galleda a sota

Catalan word order is somewhat flexible, but not every alternative sounds equally natural in every context. This version is a neutral, standard way to say it.

For example, una galleda es posa a sota is possible in some contexts, but it sounds more marked, as if you are emphasizing a bucket.

So the sentence uses the most ordinary order for this kind of impersonal statement.