Learn Hardcore German: Zu Hause habe ich einen Wasserfilter gekauft, damit ich Leitungswasser trinken kann, ohne dass es komisch schmeckt. - At home I bought a water filter so that I can drink tap water without it tasting strange.

German main clauses must have the conjugated verb in second position (the V2 rule). The first position is whatever you decide to put in front (subject, time, place, object, etc.). Here:

Zu Hause = first position (place, for emphasis)
habe = second position (the verb)
ich then comes after the verb

So both are correct, just with different emphasis:

Zu Hause habe ich … gekauft – emphasis on where you bought it.
Ich habe zu Hause … gekauft – more neutral; emphasis on I.

Why is it einen Wasserfilter and not ein Wasserfilter?

Wasserfilter is masculine in German (der Wasserfilter).

In the sentence, it is the direct object (what you bought), so it takes the accusative case. The masculine indefinite article in the accusative is einen:

Nominative: ein Wasserfilter (Ein Wasserfilter ist neu.)
Accusative: einen Wasserfilter (Ich kaufe einen Wasserfilter.)

That’s why it must be einen Wasserfilter here.

Why does it use habe … gekauft instead of a simple past like kaufte?

In modern spoken German, people usually use the present perfect (Perfekt) for past events:

Ich habe einen Wasserfilter gekauft.

The simple past (Präteritum), e.g. Ich kaufte einen Wasserfilter, is common in writing (stories, reports, newspapers) and in a few very frequent verbs in speech (like war, hatte).

So Ich habe einen Wasserfilter gekauft sounds natural in everyday conversation; Ich kaufte would sound more written, formal, or slightly old-fashioned in speech.

What exactly does damit mean here, and how is it different from um … zu?

damit introduces a purpose clause with its own subject. It means roughly “so that / in order that”:

…, damit ich Leitungswasser trinken kann
= “… so that I can drink tap water …”

um … zu is also “in order to”, but you use it when the subject of both actions is the same:

Same subject: Ich kaufe einen Wasserfilter, um Leitungswasser zu trinken.
Different subject → you must use damit:
Ich kaufe einen Wasserfilter, damit meine Kinder Leitungswasser trinken können.

In your sentence, ich is the subject in both clauses, so you could also say:

Zu Hause habe ich einen Wasserfilter gekauft, um Leitungswasser trinken zu können.

The version with damit is just more explicit and slightly more colloquial here.

Why is the word order … damit ich Leitungswasser trinken kann and not … damit ich kann Leitungswasser trinken?

Because damit introduces a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end of the clause.

So:

Main clause: Ich kann Leitungswasser trinken. (verb in second position)
Subordinate clause with damit: …, damit ich Leitungswasser trinken kann. (verb at the end)

That’s also why in the modal-verb construction trinken kann, the modal verb (kann) is the last word in the clause.

Why is Leitungswasser written as one word and with a capital letter?

German loves compound nouns. Leitung (pipe) + Wasser (water) → Leitungswasser (tap water). These are written as one word.

All nouns in German are capitalized, so:

das Leitungswasser
Leitungswasser trinken

That’s why it’s Leitungswasser, one word, with a capital L.

What does ohne dass mean, and how is it different from ohne zu?

ohne dass introduces a subordinate clause with its own subject and finite verb. It means “without (the fact that) …”:

…, ohne dass es komisch schmeckt.
= “… without it tasting weird.”

ohne zu is used when there is no new subject and you are using an infinitive:

Same subject:
Ich gehe, ohne etwas zu sagen. (= I go without saying anything.)

In your sentence, the subject of the “tasting” part is es (referring to the water), not ich, so a full clause with ohne dass fits very naturally:

…, ohne dass es komisch schmeckt.

You could rephrase with ohne zu, but you’d have to restructure the sentence (and it would sound more artificial here).

Could you also say …, ohne dass es komisch ist instead of …, ohne dass es komisch schmeckt?

You could, but it would change the nuance slightly.

ohne dass es komisch schmeckt – focuses on the taste being strange.
ohne dass es komisch ist – is more general: “without it being weird/strange” (could be taste, smell, color, idea, etc., depending on context).

Since we’re talking specifically about drinking water and using a filter, it’s natural to focus on taste, hence schmeckt.

Why is it es komisch schmeckt and not es schmeckt komisch?

Both word orders are possible and correct. In main clauses, the more common order would be:

Es schmeckt komisch.

In the subordinate clause … ohne dass es komisch schmeckt, the verb schmeckt must be final, because it’s a subordinate clause. What stays together before the verb is somewhat flexible:

… ohne dass es komisch schmeckt.
… ohne dass es schlecht schmeckt.

So here, es komisch schmeckt is simply the part of the clause that precedes the final verb. You couldn’t move schmeckt in front of komisch, because that would break the “verb at the end in subordinate clauses” rule.

Can I drop the es and just say …, ohne dass komisch schmeckt?

No. The clause ohne dass es komisch schmeckt needs a subject. Here, es refers back to Leitungswasser (or more loosely, to the water).

German doesn’t allow you to just leave out the subject in this kind of clause, so you must keep es:

Correct: …, ohne dass es komisch schmeckt.
Incorrect: …, ohne dass komisch schmeckt.

Why is the verb order trinken kann and not kann trinken?

In a main clause, you would say:

Ich kann Leitungswasser trinken.

In a subordinate clause (introduced by damit), the conjugated verb must be at the very end:

…, damit ich Leitungswasser trinken kann.

In verb clusters with a modal verb, the modal (kann) comes last, after the infinitive (trinken). So:

Subordinate: … dass ich Leitungswasser trinken kann.
Not: … dass ich Leitungswasser kann trinken. (unnatural/wrong in standard German)

What is the difference between zu Hause, nach Hause, and bei mir zu Hause?

They express different ideas:

zu Hause = at home (location)
Ich bin zu Hause. – I am at home.
nach Hause = (to) home (direction, going there)
Ich gehe nach Hause. – I’m going home.
bei mir zu Hause = at my place / at my home
Wir treffen uns bei mir zu Hause. – We’ll meet at my place.

In your sentence, Zu Hause habe ich einen Wasserfilter gekauft, zu Hause means at home (i.e. you bought it at home, probably online or from someone who came to your home).

Are the commas before damit and ohne dass required?

Yes. In German, subordinate clauses must be separated from the main clause by a comma.

Both damit and ohne dass introduce subordinate clauses, so you need commas:

Zu Hause habe ich einen Wasserfilter gekauft, damit ich Leitungswasser trinken kann, ohne dass es komisch schmeckt.

If you left them out, it would be incorrect in standard written German.

Could I replace damit with sodass or something like also ich kann Leitungswasser trinken? Would that change the meaning?

Yes, it would change the nuance.

damit expresses purpose:
…, damit ich Leitungswasser trinken kann = “… so that I can drink tap water” (goal/intention).
sodass (or so dass) usually expresses result:
…, sodass ich Leitungswasser trinken kann = “… with the result that I can drink tap water.”
It sounds more like a consequence than a planned purpose.

Using also and a new main clause:

…, also kann ich Leitungswasser trinken …
= “… so / therefore I can drink tap water …” (again: result/conclusion, not purpose).

The original damit is best if you want to say “I bought the filter in order to be able to drink tap water.”