xy plasma cutter table question

I am working on a cnc plasma cutter. I'll try to get some pix up when
the time comes. I've cut using jog under computer control, so I'm pretty
close. I'm using Vector and Cncpro, both of which seem to work very
nicely. Motor drivers are 5A Camtronics boards.

Right now I'm working on the table and work support. I'd like to cut a
variety of materials, and it seems very sensible to put a water tray
under the work to capture the particulates of metal coming off the torch
exhaust.

How deep should the water be?
How much space between the water and the work?

Any opinions or advice welcome, thanks.

Steve Smith
Loveland, Colorado