In case anyone's still confused about certain terminological matters, my understanding is this:
Wotname took "water ice" to signify a mixture of water and ice, (which I would prefer to call "water + ice" or "an ice/water mix")
... whereas as I understand it, Cavalier intended "water ice"* to signify "ice composed of frozen water"
(as opposed to some other liquid, CO2 being another obvious example .... although (red herring alert!) 'dry ice' a rather misleading term, given that "water ice" is dry to the touch once it gets colder than freezing)
*[on edit: perhaps "frozen water" would be a less confusing term?]
It's difficult to get a mixture of water and "water ice" below 0 deg C, but may not be impossible, given sufficient purity. I don't know. That observation is possibly another red herring in the real world situation, where AFAIK there are always nucleators to defeat supercooling.
But the point I'm trying to make is this, and I think a lot of lay people (like me) are under this misapprehension:
The belief that ice (frozen water) cannot be colder than 0 deg C is what I'm talking of, and this is a different matter.
If that were so, skiers would have never experienced "wild" powder snow, so light and dry that you leave no tracks (because it flows back into them, like paint
levelling) and the aerial component either hangs like smoke or just sublimes into the air rather than falling back to earth.... (ahhh, memories!)
It's complicated by the fact that snow is a good insulator, so that snow caves are warmer than staying outside whenever temp (adjusted if necessary for wind
chill) gets below zero...
but the crystals on the inside of a snowcave will soon become wet, because you're warming the air inside the cave to zero with body heat and respiration. Hence in a relatively short time, as I understand it, the superficial layer of snow insulates you from the coldness of what lies behind.
I think this, and other examples like it, is why we tend to think that ice is necessarily at freezing point, never below.
That's only true, AFAIK, when it's in the presence of liquid water - even if only a surface film, a few molecules thick.
As always, I'm open to correction on any of this, and would welcome it from anyone with the ability, time and inclination.