In peristylio parvo aqua clara in impluvio est, et puella aquam in eo spectat.

Latin often uses est by itself where English uses there is.

So:

• aqua clara in impluvio est
  literally: clear water is in the impluvium
• natural English: there is clear water in the impluvium

Latin does not need a separate word for English there in this kind of sentence.

Because there are two different prepositional phrases:

• in peristylio parvo = in the small peristyle
• in impluvio = in the impluvium

The first phrase tells you the general setting; the second tells you where the water is specifically located.

So the sentence is structured like:

• In the small peristyle,
• there is clear water in the impluvium.

Because in takes the ablative when it means in / on / inside and shows location.

Here both phrases express location:

• in peristylio = in the peristyle
• in impluvio = in the impluvium
• in eo = in it

A very important contrast is:

• in + ablative = location (in, on)
• in + accusative = motion toward (into, onto)

So if someone were going into the impluvium, you would expect in impluvium with the accusative instead.

Because the adjective must agree with the noun it describes.

Peristylio is:

• ablative
• singular
• neuter

So parvus has to match it, becoming parvo:

• peristylio parvo = in the small peristyle

This is called adjective agreement. In Latin, adjectives agree with nouns in:

• gender
• number
• case

Because aqua is in the nominative singular, which is the normal case for the subject.

So:

• aqua clara = clear water → subject
• est = is / there is

Also, clara agrees with aqua, so together they form the subject phrase:

• aqua clara = clear water

Even though English often puts the subject after there is, in Latin the subject is still simply the nominative noun.

Because its job changes.

In the first clause:

• aqua is the subject, so it is nominative.

In the second clause:

• puella aquam ... spectat
• the girl looks at the water

Here aquam is the direct object of spectat, so it must be in the accusative.

So:

• aqua = nominative singular
• aquam = accusative singular

This is one of the most basic and important patterns in Latin.

Latin adjective placement is much freer than English adjective placement.

English strongly prefers:

• small peristyle
• clear water

Latin can say:

• parvo peristylio
• peristylio parvo
• clara aqua
• aqua clara

All of these can be grammatical, depending on style and emphasis.

So the position of parvo and clara is not strange in Latin. What matters most is that the adjective agrees with the noun.

Eo means it after the preposition in.

More precisely, it is a form of the pronoun is, ea, id:

• eo = ablative singular of the pronoun

Because in here takes the ablative, the pronoun must also be ablative:

• in eo = in it

So:

• puella aquam in eo spectat = the girl looks at the water in it

In context, it most naturally refers to impluvio.

So the idea is:

• there is clear water in the impluvium
• and the girl looks at the water in it

Grammatically, a learner may notice that eo could look compatible with another earlier neuter noun as well. But the nearest and most sensible reference here is impluvium, since that is where the water is.

Because Latin has no articles.

English distinguishes:

• a girl
• the girl

Latin simply says:

• puella

The same is true for:

• aqua = water / the water
• impluvio = in an impluvium / in the impluvium

You figure out whether English needs a, an, or the from the context.

Because Latin relies much more on endings than on word order.

English depends heavily on position:

• the girl sees the water
  is different from
• the water sees the girl

Latin can move words around more freely because the endings show their roles:

• puella = subject
• aquam = object

So even if the order changes, the grammar is still clear.

Also, Latin often puts the verb at or near the end of the clause:

• puella aquam in eo spectat

That is a very normal Latin pattern.

Spectat means looks at, watches, or observes.

It comes from spectare, a verb of the 1st conjugation.

Here:

• spectat = he/she/it looks at

Since the subject is puella, it means:

• the girl looks at / watches

So spectat takes a direct object here:

• aquam spectat = she looks at the water

These are architectural terms from a Roman house.

• peristylium: a courtyard or garden area surrounded by columns
• impluvium: a basin or pool designed to collect rainwater

So the sentence describes a Roman domestic setting:

• in the small peristyle,
• there is clear water in the impluvium,
• and the girl is looking at that water.