Meine Lippe ist trocken, deshalb trinke ich mehr Wasser.

Because Lippe is a feminine noun: die Lippe.

The possessive word mein changes its ending depending on gender, number, and case. Here, Lippe is singular feminine and is the subject of the clause, so you need meine.

A quick comparison:

• mein Mund = my mouth
• meine Lippe = my lip
• mein Auge = my eye
• meine Lippen = my lips

So meine is the correct form for a feminine singular noun here.

Because trocken comes after the verb ist and describes the subject. In that position, German adjectives usually do not take endings.

This is called a predicative adjective.

• Die Lippe ist trocken.
• Das Wasser ist kalt.
• Meine Hände sind sauber.

But when an adjective comes before a noun, it does take an ending:

• eine trockene Lippe
• kaltes Wasser
• saubere Hände

So:

• die trockene Lippe = adjective before noun, with ending
• die Lippe ist trocken = adjective after sein, no ending

Meine Lippe is in the nominative case because it is the subject of ist.

• Meine Lippe ist trocken.

The thing doing the being dry is meine Lippe, so it is nominative.

Wasser is the direct object of trinke, so it is in the accusative case:

• Ich trinke mehr Wasser.

However, with Wasser, you do not see a visible change between nominative and accusative because it is a neuter mass noun and often appears in the same form.

Because the sentence contains two main clauses:

1. Meine Lippe ist trocken
2. deshalb trinke ich mehr Wasser

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

So the comma helps show the division between:

• statement/cause situation: Meine Lippe ist trocken
• result/consequence: deshalb trinke ich mehr Wasser

This is very normal in German writing.

Because German main clauses follow the verb-second rule.

That means the finite verb must come in the second position of the clause. In the second clause, deshalb takes the first position, so the verb trinke must come next:

• Deshalb trinke ich mehr Wasser.

Not:

• Deshalb ich trinke mehr Wasser. ❌

You can think of it like this:

• Position 1: deshalb
• Position 2: trinke
• then: ich mehr Wasser

This same pattern happens with many adverbs:

• Heute gehe ich nach Hause.
• Dann rufe ich an.
• Deshalb trinke ich mehr Wasser.

Deshalb means something like therefore, for that reason, or that’s why. It introduces a result or consequence.

• Meine Lippe ist trocken, deshalb trinke ich mehr Wasser.

Weil means because and introduces a reason. It is a subordinating conjunction, so it changes the word order.

Compare:

• Meine Lippe ist trocken, deshalb trinke ich mehr Wasser.
• Ich trinke mehr Wasser, weil meine Lippe trocken ist.

Important difference:

• after deshalb: normal main-clause word order, with verb in second position
• after weil: the conjugated verb goes to the end

So learners often confuse the meanings and the word order, but they work differently.

Because Wasser is being used as a mass noun in a general sense, and German often uses mass nouns without an article in that situation.

• Ich trinke Wasser.
• Ich trinke mehr Wasser.

Here, mehr means more and refers to a greater quantity.

You would use an article only in a more specific context, for example:

• Ich trinke das Wasser aus der Flasche. = a specific water
• Ich trinke mehr von dem Wasser. = more of that particular water

In your sentence, the meaning is general, so mehr Wasser is exactly what you want.

Yes. Here mehr works very much like English more.

It is being used with a noun to talk about quantity:

• mehr Wasser = more water
• mehr Zeit = more time
• mehr Geld = more money

It can also be used comparatively in other ways:

• Er trinkt mehr als ich. = He drinks more than I do.
• Das ist mehr. = That is more.

So in your sentence, mehr simply means a larger amount of water.

Meine Lippe ist trocken is grammatically correct, and it is natural if you mean one lip.

But in everyday speech, people may often say Meine Lippen sind trocken if they mean both lips are dry, because that is a more common real-life situation.

So both are possible:

• Meine Lippe ist trocken. = one lip is dry
• Meine Lippen sind trocken. = my lips are dry

A native speaker might choose the plural more often, depending on the situation, but the singular sentence is still perfectly valid.

Yes. In many everyday contexts, deshalb, deswegen, and darum can all mean something like therefore / that’s why / for that reason.

For example:

• Meine Lippe ist trocken, deshalb trinke ich mehr Wasser.
• Meine Lippe ist trocken, deswegen trinke ich mehr Wasser.
• Meine Lippe ist trocken, darum trinke ich mehr Wasser.

They are very close in meaning. The word order stays the same:

• deswegen trinke ich
• darum trinke ich
• deshalb trinke ich

So if you understand one of them, you can often recognize the others in similar sentences.