[kyzyl]

In principle it can be done, of course, but it wouldn't be economical. The abrasive sludge that accumulates in the bottom of the machine is full of large and small bits of various different materials, which complicates filtering. Even if you only cut a single material, you end up with significant amounts of abraded metal from the machine parts (slats, fittings, clamps, etc.). You would also have to spend a significant amount of energy evaporating and drying the sludge.

In any case, the main problem is that the abrasive garnet particles become decidedly less abrasive once they've been smashed into a piece of steel at 75000psi. Think of it like one of those tumblers you use to smooth and polish stones to make them pretty.

EDIT: As someone else mentioned, it's also a QC issue. Even with brand new abrasive, you sometimes get the tiniest bit of something the wrong size or weight and the solenoid feeder gets jammed and has to be take apart. Recycled sand and who knows what else would be a nightmare. Waterjets are enough work to keep running as it stands ;-)

Source: ~7 years of using an Omax waterjet cutter.