A: With flex shaft tools in general, the handpiece is not part of any electric circuit. Only the motor and foot pedal control are. Getting the handpiece wet has no impact on this, and offers no risk of electric shock. The situation might be different with some types of powered handpieces where the motor is part of the handpiece itself, such as Dremel tools or some of the micromotor types of tools. But even there, it’s likely safe, since these tools are carefully designed to isolate electric circuits from the user, whether or not there is water involved. After all, you’re holding the tool in your hand when it’s dry, so if there were any possibility of shock when wet, there’d also be some risk while dry, so these tools are double-insulated, with exposed parts electrically isolated, and usually non-conductive. And with the micromotor types of tools, many of them operate the handpiece itself on low voltage (safe) even if the control plugs into household wall current.

By the way, the insulation issues are not confined to jewelers tools. Normal power tools, drills, saws, etc, are expected to be safe to use in all sorts of conditions, including outdoor construction, where rain can occasionally be a factor. Again, the tools are designed to remain safe even if water is present. This is part of what is involved when tool manufacturers obtain UL certification for their tools. And finally, you should keep in mind that water, by itself, is not actually all that good an electrical conductor. Salt water, or water with other current-carrying ions dissolved in it, is another matter. But when you’re drilling “under water”, no doubt you’re just using tap water, which starts out clean enough, so isn’t very conductive. And, it’s also confined to a small container, so it is isolated from the environs.

The real danger of shock with water is when it’s in contact with “ground”, and can then make the electrical path from a voltage source back to ground more likely. Thus, don’t stand in a puddle and handle live wires, since your wet feet are not well insulated from ground. But this type of situation is unlikely with properly designed and undamaged electrical tools, even those with a motor in your hand and plugged into the wall (like an electric drill), because of the multiple layers of insulation built in. But as I said, your flex shaft tool is not even in this category. There’s no electric voltage or possible voltage at the handpiece. Run the thing with the handpiece under water if you want. I don’t recommend it, as this likely will allow corrosion of the handpiece, but you’d not be risking shock to do it. In drilling, set it up so the drill end itself is running under water, while the chuck and handpiece stays above water and thus, mostly dry. You’re not taking any risks in doing this.