Doug Kanter writes:

But, demineralized? I'm only up to one cup
of coffee so far, but I don't see how freezing water removes minerals.

Cascading water over a freezing plate builds up a slab that crystalizes the
water to the exclusion of solutes, which then have to be flushed. It is
discussed he

http://www.truetex.com/icemachine.htm

This is why natural ice building up in running water (like a creek) is so
clear and pure.

This principle can also concentrate dissolved things like alcohol or sugar.