Learn Hardcore Romanian: Apa este bună.

Apa is the word for “water.” In Romanian, definite articles are attached to the end of the noun. The root apă means “water” (indefinite), and the suffix -a makes it “the water.” So apa = “the water.”

Why do we say este instead of just e?

Este is the full form of the verb “to be” in the present tense (third person singular). Colloquially, Romanians often shorten it to e (e.g., Apa e bună), but este is the more formal or standard written form.

Why does bună end in -ă while apa ends in -a? They look almost the same.

They are two different letters, and here they are doing two completely different jobs.

a is the plain “a” sound, as in English “father.”
ă is a separate vowel, pronounced like the ‘a’ in “about.”
In apa, the final -a is the definite article fused onto the noun apă (“water”), giving “the water.”
In bună, the final -ă is agreement: the adjective bun (“good”) takes -ă to match a feminine singular noun.
So the two endings sit side by side in this sentence and look alike, but one of them means “the” and the other marks feminine agreement.