I have built and used a lot of wet belts for lapidary work. They work well and keep heat down, but are a lot messier than a dry grinder. They also run slower than our KMG/Bader types.
My first purchased wet grinder was a used glass grinder which is basically a two-wheel belt grinder with water spray. It had a 3X132" belt size, and stood about five feet tall. I sold it years ago, before I got back into making knives, but it was a good machine, just big. I don't think it was really conducive to doing the type of grinding knifemakers do.
Unless you want a stripe of water and rust on the ceiling, wall, floor, and yourself, it takes a lot more than a drip bucket to deal with the spray. You will need to make a shield that stops the spray and has a collection tube into a drip bucket. This will need to encase all the belt except the contact area. Everything in the grinder area will be exposed to a fine mist and high humidity, so regular rust prevention cleaning and waxing/oiling will be required. Any expensive tools, like mills, drills, band saws, and dry belt grinders, should be in another room or building. What is in the room with the wet grinder will be prone to rust. Mold and mildew will also be concerns in warmer climates. Very good 24/7 ventilation is a must.
Getting the water on the belt is the easiest part. A tin can with a tiny hole would do that, but a simple and cheap sprayer is available from many sources. Wire it to turn on and off with the grinder.
Other issues are:
They can't be used well with dust/air extraction, as the hoses and tubing will get gunked up with the damp swarf.
You will also need to purchase water-proof belts. With a good spray collection shield, belt changes are a bit more complicated.
Obviously, everything involved in the build will need to be either a non-rusting metal, or well painted. Most home built lapidary wet belt grinders have plywood cases which are fiberglassed. Sheet aluminum works well ,too.
