Answer:
Adverb: slowly
It modifies the word "water"
Step-by-step explanation:
An adverb is a part of speech that shows the degree or extent of the word it modifies. It usually modifies a noun, a pronoun or another advert in a sentence.
From the given sentence, the adverb there is "slowly" and it modifies the noun "water" by showing the degree to which the water was flowing.