Aqua deorsum e monte fluit et ad flumen pervenit.

Because aqua is the subject of both verbs: fluit and pervenit.

• aqua = water
• It is the thing that flows and reaches

So Latin uses the nominative case for the subject, just as English uses normal subject position:

• Water flows
• Water reaches the river

Deorsum means downward or downwards. It is an adverb.

It tells you how the water flows:

• Aqua deorsum fluit = The water flows downward

It does not change form, because adverbs in Latin do not agree with nouns.

Because e (or ex) means out of / from, and it takes the ablative case.

So:

• mons = mountain
• ablative singular = monte
• e monte = from the mountain

This is a very common Latin pattern:

• e/ex + ablative

Both e and ex mean the same thing here: out of / from.

Usually:

• ex is often used before vowels and sometimes before certain consonants
• e is often used before consonants

But in real Latin, there is some flexibility. In this sentence, e monte is perfectly normal.

So the important point is:

• e monte = from the mountain

It is ablative because the preposition e requires the ablative.

This is one of the most important things to learn in Latin: many prepositions always take a particular case.

Here:

• e
  • ablative
• monte is the ablative singular of mons

So e monte literally means out from the mountain.

Fluit is:

• 3rd person singular
• present tense
• from the verb fluo, fluere = to flow

So:

• fluit = he/she/it flows

Since aqua is singular, the singular verb makes sense:

• Aqua fluit = Water flows

Because pervenit is:

• 3rd person singular
• present tense
• from pervenio, pervenire = to arrive at, reach

So:

• pervenit = he/she/it arrives at / reaches

With aqua as the subject:

• aqua ad flumen pervenit = the water reaches the river

Depending on context, pervenit can also sometimes be translated arrives, but reaches works very naturally here.

Because Latin often uses ad + accusative to mean to or toward a place.

Here:

• ad = to, toward
• flumen = river
• ad flumen = to the river

Latin usually needs the preposition here to show the direction clearly.

Because ad takes the accusative case.

So:

• nominative: flumen
• accusative: flumen

This noun happens to have the same form in nominative and accusative singular because it is a neuter 3rd-declension noun.

That means the case is not obvious just from the ending, but the preposition tells you:

• ad flumen = accusative after ad

Because Latin has no articles.

English says:

• the water
• a mountain
• the river

Latin usually just says:

• aqua
• mons / monte
• flumen

Whether you translate as the, a, or sometimes no article at all depends on context.

So aqua could mean:

• water
• the water

And ad flumen could mean:

• to the river
• to a river

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

English relies heavily on position:

• Water flows from the mountain

Latin can move parts around more freely:

• Aqua deorsum e monte fluit et ad flumen pervenit

The sentence still makes sense because:

• aqua is nominative subject
• monte is ablative after e
• flumen is accusative after ad

So the order is natural Latin, even if it does not match the most basic English order exactly.

Yes. Et means and.

It connects the two verbs:

• fluit = flows
• pervenit = reaches

So the sentence has one subject, aqua, doing two actions:

1. it flows downward from the mountain
2. it reaches the river

Yes. That is exactly how it works.

The subject aqua applies to both verbs:

• Aqua fluit
• Aqua pervenit

Latin often states the subject once and then gives multiple verbs connected by et.

So you do not need to repeat aqua.

Yes, but the meaning would be a little different in nuance.

• e monte = out of / from the mountain
• de monte = down from the mountain or simply from the mountain, often with the idea of movement down from a surface or higher place

Since the sentence already has deorsum (downward), e monte works well to express the source, while deorsum expresses the downward motion.

So e monte is a good choice here.

A common classroom pronunciation would be something like:

AH-kwa deh-OR-soom eh MON-teh FLOO-it et ad FLOO-men per-WEH-nit

A few helpful points:

• aqua: kw sound in the middle
• fluit: often pronounced roughly FLOO-it
• c and g are always hard in restored classical pronunciation, though this sentence does not contain a soft/hard issue
• v in classical pronunciation is like English w, but there is no v letter here except in pervenit if spelled with v; in restored pronunciation that would sound like w: perwenit

Pronunciation conventions vary by classroom, but this gives a useful starting point.