The Rashash's question is how the Gemara intends for Mayim to be "Maveh" if the Pasuk would state "Mayim Navu Aish" (Yeshaya 64:1). The Rashash answers that the Pasuk would mean that water becomes bubbly from fire, and according the water could become a Mazik of Maveh. He states that this is in accordance with Tosfos, which means that the water would be a Mazik through Gerama and still be called a Mazik (this would be the Chidush of Maveh). The Rashash adds that Rav Mari (who asked the question) very possibly understands the Pasuk this way as it is ("Mayim Tiveh Aish"). Even so, the Rashash explains, he asked that water which is turned into bubbly/boiling water should be called "Mavin" or "Nivin" (the different name is not a problem, according to Tosfos DH "Mi Ksiv").

All the best,

Yaakov Montrose