The adjective in your sentence is “cool” and it describes the noun “waters.”
An adjective is a word that describes, or qualifies, a noun. It tells what kind, which one, or how many. A noun is a person, place, thing, or idea.
In this case, there are three nouns in your sentence: Taha, waters, and pool. Only one of them is being described with an adjective, although pool is described with an article, the, which is considered a type of adjective.
The word cool describes the waters, or tells what kind of waters they are. Adjectives are useful because they give us more detail about their nouns.