Although every waterjet model is different, there are certain standard features that will be present in all waterjets in one form or another.
Controller
The controller is the "brains" of the waterjet: it turns the high-pressure water pump on and off, moves the nozzle head and controls the abrasive flow. Most modern waterjets use a standard PC with custom software running on it. In the above picture, the computer is enclosed in a cabinet to protect it from water and abrasives.
Nozzle
The nozzle is the business end of the waterjet. High-pressure water flows into the nozzle, where it is mixed with abrasive and the combined stream then exits directly onto the material to be cut. The motion system moves the nozzle across the material.
Pump
The high-pressure water pump takes water and pressurizes it to between 40,000 and 60,000 PSI (2800 and 4,000 bar). For comparison, your garden hose can supply water at a pressure of about 60 PSI (4 bar). The pump is the major wear component of a waterjet and requires periodic maintenance to replace components. In the picture above, the pump is enclosed in a cabinet to reduce noise.
Abrasive delivery system
Abrasive, typically a hard reddish mineral called garnet is fed through a tube into the nozzle. In the nozzle it is mixed with the high-pressure water to form the water/abrasive stream that cuts through the material. The abrasive flows at a rate of between one-half and one pound per minute (0.2 and 0.5 kg/minute) and is usually gravity fed.
Motion System
The motion system moves the nozzle head along an X-Y axis. In the above picture, each axis is covered with a black bellows that can expand and contract. The bellows protects the precision gears used to position the nozzle from water and abrasive.
Catch tank
All that water and abrasive (and bits of eroded material) needs to go somewhere and that somewhere is the catch tank. The catch tank also serves to dissipate the energy of the waterjet stream so that it doesn't cut into the floor. The excess water flowing into the catch tank can be recirculated or sent to a storm drain. The spent abrasive typically accumulates in the catch tank and is periodically shoveled out.