From: Rabbi Moshe Sofer
To: Rabbi David Tzvi
The Chasam Sofer rules that snow gathered by human hands does not incur the disqualification of mayim she'uvin, because that disqualification stems from water's susceptibility to tumah — and snow, which cannot receive tumah at all, is entirely exempt from this concern. For melting snow, he permits indirect heating via hot iron or coals as merely removing an impediment rather than hovyah bidei adam, while cautioning against pouring hot water from a vessel.
Source: Shu"t Chasam Sofer YD §213