Isekai de Mizu no Dai Seirei Yattemasu.

Synopsis:

When the carefree high school student Nagi Saejima awakens from his slumber, he transforms into a lake in another universe!? Discovering that he is the "Great Spirit of Water" with the lake as his primary body, Nagi uses the power within himself to heal people who are ill or injured. One day, a boy calls out to Nagi, who is guided by a voice requesting assistance. Nagi's destiny will be drastically altered by that encounter. The much anticipated comicalize is the winner of the 2nd Next Generation Fantasy Cup "Unique Character Award" for Alphapolis! "I have to use God's healing power to save it because I was revered."