Answer:
the water in the mountain spring
Step-by-step explanation:
At the very beginning, the poet talks about the water from the springs that he hears for the first time after five years. As he is revisiting the place after these five years and he describes the waters that roll from these mountain springs as having "soft inland murmur".
In the next lines, he describes then the other things he sees around in the nature that he has not seen in five years - skies, cliffs, ground, etc.