Learn Hardcore Turkish: Çorba tuzlu olunca, ben biraz su ekliyorum. - When the soup is salty, I add a little water.

-ınca/-ince (also -unca/-ünce) is a common “when/once/if” type connector. In Çorba tuzlu olunca, it means “when/once the soup becomes salty / if the soup turns out salty.”
So the structure is:

tuzlu ol- = to be/become salty
tuzlu olunca = when it becomes salty / if it’s salty

It often describes a condition that triggers the action in the main clause.

Why is it tuzlu olunca and not just tuzlu olunca without ol-, or tuzlu olursa?

With adjectives, Turkish often uses olmak to mean “to become” (a change of state) or to form a clause more naturally.

Çorba tuzlu = “The soup is salty.” (simple statement)
Çorba tuzlu olunca = “When the soup becomes salty / when it turns out salty.” (condition/time)

tuzlu olursa is also possible but slightly different:

Çorba tuzlu olursa, ... = “If the soup is salty, ...” (more clearly a hypothetical/conditional)
Çorba tuzlu olunca, ... = often feels like “when/once it happens” or “whenever it happens.”

In everyday speech, both can sometimes overlap, but olunca frequently carries a “once/when it ends up that way” nuance.

What does ekliyorum mean exactly, and why is it in the present tense?

ekliyorum comes from eklemek = to add.

ekle- (verb stem) + -iyor (present continuous / habitual in context) + -um (I)

So ben biraz su ekliyorum means “I add a little water.”
Even though -iyor is often taught as “present continuous,” it’s also very commonly used for habitual/general actions, especially in sentences like:

“When X happens, I do Y.”

So here it’s basically: “When the soup is salty, I add a bit of water (as my usual response).”

Is ben necessary? What changes if you drop it?

It’s not necessary, because ekliyorum already shows the subject (-um = “I”). You can say:

Çorba tuzlu olunca, biraz su ekliyorum.

Including ben adds emphasis or contrast, like:

“I add water (maybe someone else does something different).”

Why is there a comma after olunca?

The comma separates the dependent clause (Çorba tuzlu olunca) from the main clause (ben biraz su ekliyorum). It’s very common in writing. In casual writing it may be omitted, and in speech there’s usually a pause.

What is the word order doing here? Could it be Ben çorbaya biraz su ekliyorum instead?

Turkish word order is flexible, but the “neutral” tendency is:

time/condition clause first (optional)
then the main clause
with the verb near the end of its clause

You can rephrase the main clause as:

Ben çorbaya biraz su ekliyorum. = “I add a little water to the soup.”

In your original, çorbaya (“to the soup”) is understood from context, but adding it is also very natural:

Çorba tuzlu olunca, ben çorbaya biraz su ekliyorum.

Different word orders mainly change emphasis, not basic meaning.

Why is it biraz su (a little water) and not biraz suyu?

Because the sentence is talking about an indefinite amount of water—some water, not a specific known portion.

biraz su = “a little water” (indefinite)
suyu would mark it as definite/identified (and often needs a clearer context), like “the water” or “that water.”

With eklemek, the thing being added is usually indefinite unless you specify it:

Biraz su ekliyorum. (normal)
Suyu ekliyorum. = “I’m adding the water.” (sounds like a specific water you already mentioned)

Does tuzlu olunca imply the soup became salty, or just that it is salty?

It can imply either depending on context, but it often suggests a result/realization:

became salty (you oversalted it)
or turns out salty (you taste it and realize it’s salty)

If you want to strongly emphasize “it is salty (state)” rather than “becomes/turns out,” you could say:

Çorba tuzluysa, ... = “If the soup is salty, ...” or
Çorba tuzlu olduğunda, ... = “When the soup is salty / when it is in a salty state” (more formal/bookish)

Could I use tuzlu olursa instead of tuzlu olunca in this sentence?

Yes, and it would still be correct, but slightly shifts the feel:

Çorba tuzlu olunca, biraz su ekliyorum.
“When/once it ends up salty, I add some water.” (common, matter-of-fact)
Çorba tuzlu olursa, biraz su ekliyorum.
“If it is salty, I add some water.” (more explicitly conditional/hypothetical)

Both are natural; olunca is very common for “when this happens, I do that.”

Why is it su eklemek and not su katmak or another verb?

su eklemek is a straightforward, common way to say “add water.”
Other options exist with slightly different tone:

su eklemek = neutral “add water”
su katmak = also “add/mix in water,” often used for adding something into a mixture
sulandırmak = “to dilute (it) with water” (more like describing the result)

In your sentence, eklemek fits perfectly because it focuses on the action of adding.

How would I make it past tense: “When the soup was salty, I added a little water”?

You’d typically use past tense in the main clause:

Çorba tuzlu olunca, biraz su ekledim.
“When the soup was/turned out salty, I added a little water.”

You can keep ben if you want emphasis:

Çorba tuzlu olunca, ben biraz su ekledim.