Sacerdos casta aquam portat.

By itself, sacerdos can mean either priest or priestess. It is a noun of common gender, so context tells you whether the person is male or female.

In this sentence, casta is feminine, so it strongly suggests that the sacerdos here is female: a chaste/pure priestess.

If the priest were male, you would expect castus sacerdos instead.

Because Latin adjectives agree with the nouns they describe in gender, number, and case—not in having the same ending.

So here:

• sacerdos = nominative singular feminine
• casta = nominative singular feminine

They match grammatically, even though they come from different declensions and therefore have different-looking endings.

This is very common in Latin. Two words can agree perfectly without looking similar.

The cases are:

• sacerdos = nominative singular
• aquam = accusative singular

That matters because:

• the nominative usually marks the subject: the person doing the action
• the accusative usually marks the direct object: the thing receiving the action

So sacerdos is the one carrying, and aquam is what is being carried.

casta is also nominative singular feminine, because it describes sacerdos.

Because aquam is the accusative singular of aqua.

The basic forms are:

• aqua = nominative singular
• aquam = accusative singular

That -m is a very common accusative singular ending in first-declension nouns. It shows that water is the direct object of portat.

Portat is a verb meaning carries or is carrying.

Its form tells you several things at once:

• 3rd person
• singular
• present tense
• active voice

So it means he/she/it carries.

Since the subject is sacerdos casta, the meaning is the chaste/pure priestess carries water.

Because classical Latin does not have articles like English the and a/an.

So sacerdos can mean:

• a priestess
• the priestess

and aquam can mean:

• water
• the water

English has to choose an article, but Latin usually leaves that to context.

Latin often puts the verb near the end of the sentence, so aquam portat is very natural Latin word order.

But Latin word order is much more flexible than English word order because the endings already show what each word is doing.

So these could all mean roughly the same thing:

• Sacerdos casta aquam portat
• Casta sacerdos aquam portat
• Aquam sacerdos casta portat

The basic meaning stays the same because the forms show the grammar. What changes is usually emphasis or style, not the core meaning.

Yes. Latin adjectives can come either before or after the noun.

So both of these are possible:

• sacerdos casta
• casta sacerdos

Both mean chaste/pure priestess. The difference is usually one of style or emphasis, not a change in basic meaning.

Sacerdos is a third-declension noun.

Its dictionary forms are:

• sacerdos
• sacerdotis

That is useful because beginners sometimes assume that a word ending in -os must belong to some other pattern. But here, sacerdos is simply a third-declension noun.

It can be broader.

Depending on context, casta can suggest ideas like:

• chaste
• pure
• morally clean
• ritually pure

In a religious setting like this one, pure or ritually pure may fit very well. So the exact shade of meaning depends on context, even though chaste is a common basic gloss.