It has little, if anything, to do with the water. Ice made in a freezer is cloudy because of air bubbles. There are techniques for making clear ice using directional freezing. Here's one way: https://altonbrown.com/recipes/cocktail-ice-cubes/
No, being able to see through it has nothing to do with water purity (unless your water is so muddy that it's not clear even as a liquid), it's to do with the formation of the ice and the incorporation of air bubbles. You can make clear ice pretty easily with molds.
I did a bit of Googling and pretty much every article on the subject of clear ice includes impurities other than air:
> The most common impurities found in tap water include lime (also known as limescale), calcium, fluoride, nitrates, magnesium and certain other organic elements that are practically impossible to remove with regular filtration methods. So, when water freezes, the impurities that were evenly distributed in the water, tend to congregate near the middle, making ice cubes the whitest at their center. [1]
> But the reality is, most of the “impurities” found in your freezer ice cube are more likely nothing more than the minerals present in your tap water. Tap water commonly contains minerals such as: Calcium, Magnesium, Potassium [2]
Do you have a citation to back up the claim that it's only air bubbles?
There are other impurities than air, but they don't contribute making the ice cloudy. The only thing making ice cloudy is the bubbles. And you can verify it experimentally in your own freezer just by using a different freezing technique to create perfectly clear ice: https://youtu.be/E1G1I1LJjrI
I don't think this video is really sufficient to prove your point that "the only thing making ice cloudy is the bubbles". The directional freezing technique is essentially a filtration method - the H2O freezes first into the growing crystalline structure and all the other impurities (various minerals AND dissolved air) get "pushed down" and concentrated into the liquid water below.
As evidence that directional freezing can filter out impurities other than air, I would point out that the directional freezing process is an effective enough filtration method to filter salt out of sea water in sea ice. [1] So my assumption is that those other minerals commonly found in water (lime, calcium, fluoride, magnesium, etc) are also being filtered out in the process - and it certainly seems plausible to me that filtering those out contributes to the clarity of the resulting ice.
So my intuitive understanding, along with what I could learn with a bit of googling, is that there are a number of impurities which can make ice appear cloudy including (but not limited to) dissolved air. A number of people here seem to be adamant that it's just air bubbles, so I'd honestly like to know why they believe that to be true (e.g. sources, some clear explanation, etc)? So far the only justification I've seen is "because directional freezing works" - but as explained above I really don't see that as being a sufficient justification since it filters out a number of impurities other than air.
When you said the water was "impure" in your previous comment, no one thought you meant it was sullied with... air. While not technically incorrect, if you honestly thought "impure" was a good way to describe water with air dissolved in it, the best I can say is to watch out for your subtext when using a word much differently than basically anyone else does.
I don’t think referring to dissolved gas in water as an impurity is all that uncommon. To quote wikipedia:
> Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. [1]
Other sources list carbon dioxide, oxygen, and nitrogen as impurities that can cause corrosion in pipes [2], or can form bubbles in systems where there are major changes in pressure or temperature, blocking pumps, fine tubing, filters, etc. [3]
So it’s a bit context dependent, but there are situations where it is totally reasonable to view dissolved gases in water as an impurity. And this context - the discussion of what makes ice clear or cloudy - is one of them.
How can you claim so confidently that “no one thought” something, or that the parent is “using a word much differently than basically anyone else”? If you honestly think that you speak for all 1.35 billion English speakers in the world - or even all the people reading this thread - the best I can say is speak for yourself.
Yes, I used very slight hyperbole with "no one". Counterexample found, film at 11. A few highly technical contexts don't change the point: If someone holds up a flask of water and says "this is impure", what's at the top of the list of possible impurities in your mind, and how far down the list is air?
If by purity you mean any sort of "alien substance" whatsoever, stick with liquid water. And I hope you don't like any colored minerals, as those all have "alien substances" inside.
(The freezer, of course, has nothing to do with this - it's the water you're putting into it that's impure.)