The invention relates to abrasive water jet systems comprising an abrasive water jet mixing tube having a longitudinal bore lined with a superhard material, including such systems which use cubic boron carbide (CBN), diamond, or other materials with a hardness greater than that of alumina as the abrasive material. The invention also comprises methods of using an AWJ system having a mixing tube having a longitudinal bore lined with a superhard material. Some embodiments include AWJ mixing tubes comprised of a plurality of connected components. Such connections may be disconnectable.