Not such fancy equipment. I used to make it in a lunchbox cooler with our very hard tap water; that eventually cracked but I have been rocking one of these for a decade now.

www.clearlyfrozen.com

All you need is directional freezing. My ice comes out crystal clear in big ol’ blocks like that.

To be fair - I would charge $5 a tray too. It takes a day & a half and space in my freezer. But it is an easy, cheap, and fun hobby