So a lot of us out there have anecdotes where a teacher at school melts a bunch of snow in a glass to prove the point that kids shouldn't eat snow.  I think that witnessing this demonstration is a "rite of passage" in one's early primary school years.

One of my students was eating a snowball out on the playground today.  I got the snowball from him, and decided to stick it in a baggie to prove the point that he shouldn't be eating the snow.

After a half hour the snow wasn't melting quickly enough, so I sealed up the baggie and put it in the microwave.  Do you know what I got after microwaving it?

A baggie full of clean, clear, seemingly potable water.  I was surprised. 

I told the kids with a smile, "Okay.  Eat all the snow you want."