Learn Hardcore Turkish: Ben bardağı suyla doldurabilmek için musluğu açıyorum. - I am turning on the tap to be able to fill the glass with water.

No, you don’t have to. The ending -um in açıyorum already marks first-person singular, so Ben is optional. You include Ben for emphasis or contrast (e.g., “I’m the one opening it”).

Why is it bardağı with the accusative -ı?

Because the glass is a definite, specific direct object (“the glass”). In Turkish, definite/specific direct objects take the accusative:

Definite: Bardağı dolduruyorum.
Indefinite: Bir bardak dolduruyorum. (no accusative)

Why is musluğu also in the accusative?

It’s the direct object of the main verb açmak (“to open”), and it’s specific (“the tap/faucet”). If you meant an unspecified one, you’d say Bir musluk açıyorum.

What exactly does suyla mean and how is it formed? Can I say su ile?

Suyla = su (water) + buffer y + instrumental/comitative suffix -la (“with/by means of”). It literally means “with water.”
Yes, su ile is the spaced form and is a bit more formal. In speech, ile commonly fuses to -la/-le. The buffer y appears because the word ends in a vowel.

Why not suyu instead of suyla?

Suyu is the accusative of “water” and would make “water” a direct object (“the water”). You don’t “fill the water”; you fill the glass. With “fill X with Y,” Turkish typically marks the container as the object and puts the content in instrumental: bardağı suyla doldurmak.

Can I also say Bardağa su doldurmak?

Yes. Turkish has two common patterns:

X-ı Y-la doldurmak = fill X with Y (container accusative + content instrumental): Bardağı suyla dolduruyorum.
X-a Y(ı) doldurmak = fill Y into X (container dative + content as object/indefinite): Bardağa su dolduruyorum. / Bardağa suyu dolduruyorum (if “the water” is specific).

Why use doldurabilmek için instead of simply doldurmak için?

Adding -ebil- (ability/possibility) emphasizes enabling the action: “in order to be able to fill.” Without it—doldurmak için—it’s the straightforward “in order to fill.” Both are grammatically correct; the version without -ebil- is often more neutral.

Will it be wrong if I drop -ebil- here?

Not at all. Ben bardağı suyla doldurmak için musluğu açıyorum is perfectly natural. Using -ebil- adds a slight nuance of making the filling possible.

How flexible is the word order?

Turkish is quite flexible. Common variants (all correct) include:

Ben bardağı suyla doldurabilmek için musluğu açıyorum. (original)
Bardağı suyla doldurabilmek için musluğu açıyorum. (drop “Ben”)
Suyla bardağı doldurabilmek için musluğu açıyorum. (emphasizes “with water”)
Musluğu, bardağı suyla doldurabilmek için açıyorum. (fronts “musluğu” for focus) Purpose phrases with için typically come before the main verb, but placing them at the end is also heard in speech.

What is the morphological breakdown of doldurabilmek?

dol- = become full (intransitive root)
-dur- = causative (“make become full” → transitive “fill”)
-abil- = ability/possibility (“be able to”)
-mek = infinitive/verb-noun
So: dol-dur-a-bil-mek → “to be able to fill.”

How is açıyorum formed?

aç- = open
buffer vowel -ı- (for phonotactics, chosen by vowel harmony)
-yor = present continuous marker (fixed as -yor)
-um = 1st person singular
So: aç-ı-yor-um → “I am opening.”

How do I pronounce ğ in bardağı?

Turkish ğ (yumuşak g) is not a hard “g.” It lengthens the preceding vowel or creates a gentle glide. Bardağı is pronounced roughly like “bar-da-a(ɯ),” with the “a” slightly lengthened before the final ı.

Why does bardak become bardağı and musluk become musluğu?

Two things happen:

Consonant softening: final k becomes ğ when a vowel-initial suffix is added (bardak → bardağı, musluk → musluğu).
Vowel harmony chooses the right accusative vowel: -ı/-i/-u/-ü matches the last vowel of the stem (a → ı; u → u).

Does açıyorum mean right now, or can it be habitual?

Primarily it’s present continuous (“I am opening [now]”). Turkish also uses -yor for near-future or ongoing contexts. For habits/generics, the aorist (açarım) is more typical: Bardağı doldurmak için musluğu açarım (“I open the tap to fill the glass,” as a routine).

Is there another way to express the purpose clause besides -mek için?

Yes. A common alternative is with ki + optative:

Musluğu açıyorum ki bardağı suyla doldurabileyim. (“I’m opening the tap so that I can fill the glass with water.”) You can also hear … diye: Bardağı suyla doldurayım diye musluğu açıyorum, which feels more colloquial.