1. El aqua de esos rios esta contaminada (posible)

my answer?

Es posible que ela aqua de esos rios esta contaminada.

is it el or ela agua

First of all, it is not "q" but "g" in the word "agua." There are accents that MUST be there. I corrected this one early today.

Es posible que el agua de esos ríos esté contaminada.

the word agua is feminine BUT for sound it uses the "el" when it is singular. el agua, las aguas

Sra

The correct word is "el" agua, not "ela" agua. In Spanish, "el" is the masculine article used before masculine nouns, while "la" is the feminine article used before feminine nouns. However, the word "agua" is considered a special case. Even though it is a feminine noun, it takes the masculine article "el" when singular to avoid the clash of two consecutive "a" sounds (la agua). So, the correct sentence would be: "Es posible que el agua de esos ríos esté contaminada."