Mein Mund ist trocken, deshalb trinke ich ein Glas Wasser.

Because Mund is a masculine noun in German: der Mund.

The possessive word mein changes its form depending on gender, case, and number:

• mein Mund = my mouth
• meine Hand = my hand
• mein Glas = my glass
• meine Hände = my hands

Here, Mund is masculine singular and is the subject of the sentence, so mein is the correct form.

In German, all nouns are capitalized, not just names.

So in this sentence:

• Mund
• Glas
• Wasser

all begin with capital letters because they are nouns.

This is a basic spelling rule in German.

Because trocken is a predicate adjective here. After verbs like sein (to be), adjectives usually do not take endings.

So:

• Der Mund ist trocken.
• Das Wasser ist kalt.
• Das Glas ist leer.

But adjectives do take endings when they come before a noun:

• ein trockener Mund
• kaltes Wasser
• ein leeres Glas

So in your sentence, trocken stays in its basic form because it comes after ist.

Because the sentence contains two main clauses:

• Mein Mund ist trocken
• deshalb trinke ich ein Glas Wasser

In German, main clauses are often separated by a comma when they are linked like this.

So the comma helps show the relationship:

• first clause: the situation
• second clause: the result

You can think of deshalb as meaning therefore / that's why / for that reason.

Because German main clauses follow the verb-second rule, often called V2.

That means the conjugated verb must come in the second position of the clause.

In the clause:

• deshalb = position 1
• trinke = position 2
• ich = comes after the verb

So:

• Deshalb trinke ich ein Glas Wasser. ✅
• Deshalb ich trinke ein Glas Wasser. ❌

This is very common in German. If you begin a sentence or clause with something other than the subject, the verb still stays second:

• Heute trinke ich Wasser.
• Jetzt gehe ich nach Hause.
• Deshalb trinke ich ein Glas Wasser.

Yes, absolutely.

Both are correct:

• Deshalb trinke ich ein Glas Wasser.
• Ich trinke deshalb ein Glas Wasser.

The difference is mostly about emphasis.

• Deshalb trinke ich ... puts more focus on therefore / for that reason
• Ich trinke deshalb ... starts more neutrally with the subject

In both cases, German still follows the normal word-order rules.

Because Glas is a neuter noun: das Glas.

After trinken, the direct object is in the accusative case. The accusative article for ein changes like this:

• masculine: einen
• feminine: eine
• neuter: ein

So:

• Ich trinke einen Kaffee. (Kaffee is masculine)
• Ich trinke eine Limonade. (Limonade is feminine)
• Ich trinke ein Glas Wasser. (Glas is neuter)

That is why ein is correct here.

Because in ein Glas Wasser, the important counted item is Glas.

German often uses this pattern with containers, amounts, and portions:

• ein Glas Wasser
• eine Tasse Kaffee
• eine Flasche Milch
• ein Stück Kuchen

The second noun often appears without an article, especially with uncountable substances like Wasser, Milch, or Kaffee.

So ein Glas Wasser means a glass of water.

The whole phrase ein Glas Wasser functions as the direct object of trinke, so it is in the accusative.

The most important part for case marking is ein Glas:

• Ich trinke ein Glas Wasser.

Because Glas is neuter, the accusative looks the same as the nominative: ein Glas.

The word Wasser names what is in the glass. For a learner, the easiest way to think about it is:

• ein Glas = the accusative object
• Wasser = what kind of glass / what it contains

So you mainly need to make sure Glas has the correct article.

Not exactly.

• deshalb means therefore / that's why / for that reason
• weil means because

They express a similar idea, but the sentence structure is different.

With deshalb, you have a main clause:

• Mein Mund ist trocken, deshalb trinke ich ein Glas Wasser.

With weil, you introduce a subordinate clause, and the verb goes to the end:

• Ich trinke ein Glas Wasser, weil mein Mund trocken ist.

So the meaning is similar, but the grammar is different.

Yes, it is understandable and natural enough.

German can describe body parts as trocken:

• Mein Mund ist trocken.
• Meine Lippen sind trocken.
• Meine Haut ist trocken.

Depending on context, native speakers might also say things like:

• Ich habe einen trockenen Mund.
• Ich habe Durst. = I am thirsty.

But your original sentence is perfectly fine grammatically and makes good sense.

Because the verb trinken is being conjugated for ich in the present tense.

The present-tense forms are:

• ich trinke
• du trinkst
• er/sie/es trinkt
• wir trinken
• ihr trinkt
• sie/Sie trinken

So in the sentence:

• deshalb trinke ich ...

the form trinke matches ich.

Yes. All three can often mean therefore / that’s why / for that reason in everyday German.

You could say:

• Mein Mund ist trocken, deshalb trinke ich ein Glas Wasser.
• Mein Mund ist trocken, deswegen trinke ich ein Glas Wasser.
• Mein Mund ist trocken, darum trinke ich ein Glas Wasser.

They are very similar in meaning. For a learner, the most important grammar point is that when one of these words starts the clause, the verb still comes second:

• Deshalb trinke ich ...
• Deswegen trinke ich ...
• Darum trinke ich ...