A waterjet is simply water pushed through a small opening at a high pressure. The most extreme waterjets can cut through metal while a home pressure washer to clean siding is also a form of waterjet. Waterjets can be very expensive because of the components involved, but you can save money by creating your own waterjets at home. The pressures for home applications are on the level of a pressure washer or a cutting waterjet that can slice through foam rubber.
Determine the reason for the waterjet, as that discerns the type of nozzle. A power washer needs a spray that covers a wider area. A waterjet cutter requires a small jet only a few millimetres wide.
Connect the water pump to a water supply. The incoming water pressure is small enough that you do not need to connect it using the more expensive high-pressure fittings.
Connect the hose to the high-pressure water pump using the high-pressure fittings. The shorter and thinner the hose, the more pressure at the nozzle.
Fabricate the nozzle by taking it to a fabricator. You can use an already made nozzle, such as from a hardware store, and have an adaptor created for it or you can have a nozzle created with a fabrication machine. A cutting waterjet nozzle will be a piece of metal with a thin shaft through the centre, perhaps on a few millimetres in width. This will shoot out a very thin line at extremely high pressure, which is ideal for cutting. For a pressure washer waterjet, the shaft should be thin at the bottom and slowly widen at the end. This creates a high pressure jet that creates a wide, high-speed spray.
Connect the nozzle to the hose using the high pressure fittings. Turn on the water pump and the water should come out of the nozzle at the specified pressure.
High-pressure jets of water can be dangerous. A waterjet cutter can cut through skin and bone at a high enough pressure. The water can also cause slipping, which can involve an injury.