Postea serva dicit aquam per compluvium in impluvium cecidisse, sed pavimentum iam siccum esse.

Because after dicit Latin uses indirect statement very often.

In English, we say:

• The slave-woman says that the water fell ...
• ... but that the floor is already dry.

In Latin, instead of that + finite verb, you usually get:

• an accusative subject
• plus an infinitive

So:

• aquam ... cecidisse = that the water fell / has fallen
• pavimentum ... siccum esse = that the floor is dry

This construction is often called the accusative-and-infinitive construction.

In a normal direct sentence, yes, aqua would be nominative:

• aqua cecidit = the water fell

But in indirect statement, the subject of the infinitive goes into the accusative. So:

• aquam cecidisse = that the water fell

The same thing happens with:

• pavimentum ... siccum esse = that the floor is dry

Here pavimentum is also the subject of an infinitive, so it is accusative.

It is another indirect statement, parallel to aquam ... cecidisse.

So the whole sentence contains two reported statements after dicit:

1. aquam per compluvium in impluvium cecidisse
2. sed pavimentum iam siccum esse

Literally:

• The slave-woman says the water to have fallen through the compluvium into the impluvium, but the floor already to be dry.

More natural English:

• Later the slave-woman says that water fell through the compluvium into the impluvium, but that the floor is already dry.

Because siccum agrees with pavimentum.

• pavimentum is neuter singular
• so the adjective must also be neuter singular
• therefore: siccum

If the noun were masculine, you might get siccus; if feminine, sicca.

So:

• pavimentum siccum = the dry floor
• in indirect statement: pavimentum siccum esse = that the floor is dry

Because the verb cado, cadere, cecidi has an irregular perfect stem.

Its principal parts are:

• cado = I fall
• cadere = to fall
• cecidi = I fell / have fallen

The perfect infinitive is built from the perfect stem, so:

• cecidi → cecidisse

This means to have fallen.

So aquam ... cecidisse literally means the water to have fallen.

Cecidisse is the perfect active infinitive.

After a verb like dicit, it usually shows action earlier than the saying. So:

• dicit aquam cecidisse = she says that the water fell / has fallen / had fallen

Which English tense sounds best depends on context. In this sentence, the idea is that the falling happened before the servant speaks.

By contrast:

• esse is a present infinitive
• so pavimentum iam siccum esse means that the floor is already dry, describing a state current at the time of speaking

These are architectural terms from a Roman house.

• compluvium: the opening in the roof of the atrium through which rainwater can come in
• impluvium: the basin or pool below that collects the rainwater

So:

• per compluvium = through the roof opening
• in impluvium = into the basin

These two words are often learned together because they describe matching parts of the same house design.

Because the prepositions show different relationships:

• per
  • accusative = through
• in
  • accusative = into (motion toward/into)

So the water:

• falls through the opening in the roof
• then falls into the basin below

That is why Latin uses two different prepositions here.

Iam means already.

So:

• pavimentum iam siccum esse = that the floor is already dry

It suggests that although water did fall earlier, the floor is no longer wet now. This fits well with sed:

• water did fall,
• but the floor is already dry.

Because serva is the subject of dicit.

• serva = slave-woman, maidservant
• nominative singular: serva
• verb: dicit = says

So:

• serva dicit = the slave-woman says

A learner might confuse serva with the imperative of servo (save!), but here the form is clearly the noun serva because it functions as the subject of the sentence.

Latin word order is more flexible because the endings show the grammatical roles.

English depends heavily on word order:

• The slave-woman says that the water fell ...

Latin can move words around more freely:

• Postea serva dicit aquam ... cecidisse, sed pavimentum iam siccum esse.

Some reasons for the order here:

• Postea comes first to set the time: later
• serva dicit introduces the reporting verb early
• the two indirect statements come after dicit
• sed neatly introduces the contrast

So even though the order is not English-like, the grammar is clear from the forms.

Sometimes Latin can use quod clauses, especially in later Latin or in certain contexts, but the standard and very common classical construction after a verb of saying like dicit is the accusative + infinitive.

So in a sentence like this, aquam ... cecidisse and pavimentum ... siccum esse are exactly what you would expect.

For a learner, the important pattern is:

• dicit
  • accusative subject
    • infinitive

That pattern is one of the most important features of Latin syntax.

A good way is to divide it like this:

• Postea = later
• serva dicit = the slave-woman says
• aquam per compluvium in impluvium cecidisse = that water fell through the compluvium into the impluvium
• sed = but
• pavimentum iam siccum esse = that the floor is already dry

So the basic structure is:

• Later the slave-woman says [statement 1], but [statement 2].

This kind of chunking is very helpful when reading Latin indirect statement.