On Waterjets

Doug is right about the waterjet pump, it is called an intensifier.
Typical setup uses a 3 stage mechanical pump, intensifier, and
attenuator. There is a website that shows the cutaway view and how it
works and all.

http://www.seas.smu.edu/rcam/research/waterjet/par3.html

Waterjets have some really neat aspects about them and they are
fascinating machines. I have been waiting for a "portable" one to come
out, so I started doing some research.
My conclusion is that "portable" waterjets are still many years, if
not decades away. The real cutting action is obtained by adding
pulverized garnet and other semi-precious powders. This is expensive.
A non-abrasive water jet with just water won't cut much more than fabric
or food. There are alot of them in the fish processing industry.
The powdered garnet and saphire is some of the most harmful abrasive
known. You thought your plasma was messy.
The smallest waterjet I have found to date uses a 40 horsepower
deisel and occupies the space of the average 1 car garage.

But on a positive note, here is a really cool portable tool that is
for sale now. It is a cordless MIG welder called GO-WELD. I can't
remember if it was shown on this site before. There are also already
several knock-offs like the Century.

http://brwelder.com/century/New_Folder/century.htm