Most systems will let you raise and lower the water on demand so that you can quickly move from cutting above water to cutting below water.
Cutting under water provides two main advantages:
- Reduced Noise
The water exits the nozzle at close to the speed of sound and creates a very loud noise. This noise is dramatically reduced when cutting under water.
- Reduced Mess
Even when you use a muff on the nozzle, there will still be stray splashes of water as the jet bounces off the material or the slats. Cutting under water eliminates water splashes.
If you are cutting above water, always wear hearing protection.
Cutting above water has its own advantages:
- You can easily see what is going on
- Material that floats, won’t float around
- Your material will get somewhat less wet
Beginners typically prefer to cut above water because it allows them to see the cutting process, which is both fun to watch, and also a comfort when you’re not totally sure you know what you are doing.
Thin material that tends to float, or be pushed around by the backsplash when under water, will also benefit from being cut above water. If the material is very thick, more than 2″ (5 cm) or so, you may also have to cut above water, just because you won’t be able to raise the water enough to cover the material.
Of course, being able to cut underwater, then lower the water quickly to check on progress, then raise the water again is a handy feature to have.
One other unusual benefit to cutting under water that is a bit counterintuitive, is that parts rust less when submerged. This is because being underwater prevents the constant splash of water, and then air, then water, then air, that will accelerate the rusting process over simply cutting the entire thing submerged. Another advantage of underwater cutting, is that in some cases it can reduce the amount of frosting at the edge of the cut.