I'd guess that some sort of acid is necessary, distilled water is a way to use an acid without really using an acid.

It sounds like it can be difficult to catch the crystals as they like to melt back into the water. It's also possible (likely IMO) that this method isn't effective with cactus brews made via blender (or other methods that yield a very sludgy tea.

I'm a bit skeptical myself, but it certainly sounds worth experimenting with.