I have heard of the following procedure intended to make water cleaner:
- Put a pot of water in the freezer.
- After a few hours the water will be partly frozen. Discard the ice. Keep the liquid in the freezer.
- After a few more hours the water will be, again, partly frozen. Discard the liquid. Then melt the remaining ice and use it for drinking.
I'm not sure what cleaner means, considering that tap water is perfectly good for drinking where I live. Although it seems reasonable that different solubles would have different concentrations in ice and in remaining liquid, possibly depending on mass or solubility. On the other hand I see no reason why this would discard more harmful substances than useful ones.
Can concentrations of solubles be significantly altered using such method? Can these changes have an effect on the quality of water?