Wenn meine Mitbewohnerin das Waschbecken so gründlich putzt, sieht das Bad aus, als wäre es neu.

Wenn can mean both if and when/whenever, depending on context.

In this sentence, because both verbs are in the present tense and the sentence sounds like a general situation, wenn most naturally means when or whenever:

Wenn meine Mitbewohnerin das Waschbecken so gründlich putzt, ...
= When/Whenever my roommate cleans the sink so thoroughly, ...

It could also be understood as if in some contexts, but here the habitual reading is very natural.

English speakers often mix these up.

• wenn introduces a subordinate clause meaning if or when
• wann means when? in a question or indirect question

So:

• Wenn sie putzt, ... = When/If she cleans, ...
• Wann putzt sie? = When does she clean?
• Ich weiß nicht, wann sie putzt. = I don’t know when she cleans.

This sentence needs wenn because it introduces a condition/time clause, not a question.

Mitbewohnerin means female roommate or female flatmate/housemate.

It is built from:

• mit- = with
• Bewohner = resident/occupant
• -in = feminine ending

So:

• der Mitbewohner = male roommate
• die Mitbewohnerin = female roommate

Because the clause begins with wenn, and wenn creates a subordinate clause. In German subordinate clauses, the conjugated verb usually goes to the end.

So:

• meine Mitbewohnerin putzt das Waschbecken = normal main clause
• wenn meine Mitbewohnerin das Waschbecken putzt = subordinate clause, so putzt moves to the end

That is why you get:

Wenn meine Mitbewohnerin das Waschbecken so gründlich putzt, ...

In German main clauses, the conjugated verb must be in the second position. This is called the V2 rule.

Here, the whole wenn-clause comes first and takes up position 1:

Wenn meine Mitbewohnerin das Waschbecken so gründlich putzt, = position 1

So the verb of the main clause must come next:

sieht = position 2

Then comes the subject:

das Bad

So:

Wenn ..., sieht das Bad aus, ...

This is completely normal German word order.

This is the separable verb aussehen, which means to look or to appear.

In a main clause, separable verbs split:

• Das Bad sieht neu aus.
• infinitive: aussehen
• finite form: sieht
• prefix: aus

So sieht ... aus together means looks.

That is why:

Das Bad sieht aus, als wäre es neu.
= The bathroom looks as if it were new.

Here als means as if.

So:

als wäre es neu
= as if it were new

This is a special use of als. It is not the same as:

• als = than
• als = when in the past for a one-time event
• als = as

In this sentence, it introduces a comparison with an unreal or imagined situation: the bathroom looks as if it were new.

Because German often uses Konjunktiv II after als when expressing something that only seems true, not something being stated as a fact.

• wäre is the Konjunktiv II form of sein
• als wäre es neu = as if it were new

This matches English very closely:
as if it were new, not as if it is new

So the sentence is not saying the bathroom really is new. It only gives that impression.

Es refers to das Bad.

• das Bad is neuter
• the matching pronoun is es

So:

das Bad ... als wäre es neu
= the bathroom ... as if it were new

gründlich means thorough or thoroughly.

so gründlich means so thoroughly.

The word so adds emphasis and helps set up the result in the second part of the sentence:

If/When she cleans the sink so thoroughly, the bathroom looks as if it were new.

Without so, the sentence would still be grammatical:

Wenn meine Mitbewohnerin das Waschbecken gründlich putzt, ...

But so makes the degree of thoroughness more noticeable.

Here are the main ones:

• meine Mitbewohnerin = nominative, because she is the subject of putzt
• das Waschbecken = accusative, because it is the direct object of putzt
• das Bad = nominative, because it is the subject of sieht aus

So the structure is:

• who cleans? → meine Mitbewohnerin
• what does she clean? → das Waschbecken
• what looks new? → das Bad

Yes. In everyday German, das Bad often means bathroom.

Depending on context, it can mean:

• bath
• bathroom
• sometimes even spa or bathhouse in other contexts

In this sentence, das Bad clearly means the bathroom.

You could also say das Badezimmer, which is more explicit, but das Bad is very common and natural.

Yes.

German requires commas around these clause boundaries:

Wenn meine Mitbewohnerin das Waschbecken so gründlich putzt,
comma after the wenn-clause

..., sieht das Bad aus, als wäre es neu.
comma before the als-clause

So both commas are necessary.

Yes. A very common alternative is:

Das Bad sieht wie neu aus.
= The bathroom looks like new.

That version is simpler and very idiomatic.

The original sentence with als wäre es neu is a bit more explicit and slightly more literary or elegant:

• wie neu = like new
• als wäre es neu = as if it were new

Both are good, but they are not exactly the same in style.

Yes. If the main clause comes first, it follows normal main-clause order:

Das Bad sieht aus, als wäre es neu, wenn meine Mitbewohnerin das Waschbecken so gründlich putzt.

But this version sounds a little less natural than the original, because the wenn-clause feels like background information that fits well at the beginning.

The original sentence is very natural:

Wenn meine Mitbewohnerin das Waschbecken so gründlich putzt, sieht das Bad aus, als wäre es neu.