Si puella iterum sitiet, ancilla ei aquam e puteo afferet.

Because each one is the subject of a different verb.

• puella is the subject of sitiet: the girl will be thirsty
• ancilla is the subject of afferet: the maidservant will bring

So the sentence has two clauses:

• Si puella iterum sitiet = If the girl is thirsty again / will be thirsty again
• ancilla ei aquam e puteo afferet = the maidservant will bring her water from the well

Si means if.

It introduces the conditional clause, the part that gives the condition:

• Si puella iterum sitiet = If the girl becomes thirsty again

The rest of the sentence is the result:

• ancilla ei aquam e puteo afferet = the maidservant will bring her water from the well

No. This is a very common point of confusion.

sitiet is not from esse (to be). It is from sitire / sitio, meaning to be thirsty.

So:

• sit = may be / let him-her-it be or is in certain forms of esse
• sitiet = he/she/it will be thirsty

Here sitiet means she will be thirsty.

Sitiet is future indicative, third person singular.

Latin can use the future in both parts of a future condition:

• Si ... sitiet = If ... she will be thirsty
• ... afferet = ... she will bring

In natural English, we usually do not say If the girl will be thirsty, the maid will bring... We normally say:

• If the girl is thirsty again, the maid will bring her water

But Latin often uses the future more directly here.

Iterum means again, and it modifies sitiet.

So puella iterum sitiet means:

• the girl will be thirsty again

As an adverb, iterum is fairly flexible in position. Latin word order is not as fixed as English word order.

Ei is the dative singular form of the pronoun is, ea, id.

Here it means to her or for her.

So:

• ei aquam afferet = she will bring water to her

It is not eam, because eam would be accusative, used for a direct object. But here the girl is not the thing being brought; she is the person receiving the water.

So the roles are:

• aquam = the thing brought → direct object → accusative
• ei = the person receiving it → indirect object → dative

By form alone, yes. Ei can mean:

• to him
• to her
• to it

The form itself does not tell you gender here. The context does.

Since the earlier noun is puella (girl), the natural meaning is to her.

Because it is the direct object of afferet.

The maidservant is bringing water, so water is the thing directly affected by the verb:

• ancilla aquam afferet = the maidservant will bring water

That is why aqua becomes aquam.

E means out of or from, and it takes the ablative case.

So:

• puteus = well
• puteo = ablative singular
• e puteo = from the well

This shows the source of the water.

Both e and ex mean out of / from.

Very often:

• e is used before consonants
• ex is often used before vowels or h

So e puteo is perfectly normal.

You should think of e and ex as two forms of the same preposition.

Latin word order is much freer than English word order because the endings show the grammatical roles.

English depends heavily on position:

• The maid brings the girl water

Latin can move words around more easily because case endings and verb forms already show who is doing what.

In this sentence:

• puella is nominative
• ancilla is nominative
• ei is dative
• aquam is accusative
• puteo is ablative after e
• sitiet and afferet tell you the verbs and their subjects

So even if the order changes, the meaning can remain the same.

A very literal version would be something like:

• If the girl will be thirsty again, the maidservant will bring water to her from the well.

But natural English usually says:

• If the girl is thirsty again, the maid will bring her water from the well.

So the main differences are:

• Latin uses future forms more directly in this kind of condition.
• English usually uses present tense after if.
• Latin word order is freer.

It comes from afferre, meaning to bring to, to carry to, or simply to bring.

Its principal parts are commonly given as:

• affero, afferre, attuli, allatum

So afferet means he/she/it will bring.

Here:

• ancilla ... afferet = the maidservant will bring

This verb is slightly irregular because it is built from ad + fero.