Take ordinary tap water and pressurize it to 60,000/55,000 psi (4,000 bar) and force it through a very small hole. Mix the water with garnet abrasive and you have a very thin stream of water traveling very fast that will rapidly erode most materials. Some waterjets are "pure waterjets" and don't add the garnet abrasive. These are used to cut softer materials, such as food, rubber, and foam.