Nolin, who studies snow and ice in the climate system, says most snow is just as clean as any drinking water. To make their way from a cloud to the ground, cold water molecules have to cling to particles of dust or pollen to form the ice crystals that then grow into snowflakes in a process called deposition. These, Nolin points out, are the same tiny particles we normally breathe. Plus, as snowflakes fall, they have a harder time picking up soot and other air pollutants than raindrops, which are better at picking up these particulates.