And quite simple to make.
You will need (preferably) one of those silicone ice cube trays in the larger size. They can be obtained online (Amazon,etc.) or at stores that sell home goods, like Crate & Barrel.
Remember the cleaner and purer the water, the clearer the cube.
I boil filtered water and let it cool to make mine.
Simply place clean, organic (non-sprayed) flowers in each quadrant, and pour the water over them, being sure to cover them completely.
Pop them in the freezer and freeze.
This can be done with flowers, herbs, fruit pieces, whatever strikes your fancy. Bear in mind that as it melts in the drink, whatever is in the cube will end up in your drink ...
that is if you sip slowly!