For this project, you'll need a site with access to electricity, a small recirculating pump (choose the smallest one available; you'll need only gentle water pressure), and two grindstones measuring about 16 and 23 inches in diameter (look for them at salvage yards and landscaping companies).
1. Prepare the liner. For the base of the water feature, purchase a shallow whiskey-barrel liner slightly bigger in diameter than the large grindstone. This will allow water to run over the grindstones and back into the liner. The liner must be deep enough for the water pump to be immersed. Once you've chosen a location, dig a hole deep enough to sink the liner so it's flush with the ground. Set the liner in the hole, checking to make sure it is level. Add soil around the liner to hold it in place. Clean up any soil you spill in the liner.
2. Add the pump. Place the water pump in the center of the liner. Place river rock or chipped brick under and around the pump, lifting it so it is about level with the top of the liner and securing it in place. Lay a board across the top of the liner. Mark the location where the board matches up with the pump and cut a hole at that spot. Notch the ends of the board to set down over the liner; set the board in place.The board will help guide the position of the grindstones and will distribute the weight of the stones so they won't crush the liner.
3. Position the grindstones over the board, making sure their holes match up with the hole in the board and with the pump. Fill the liner with water.
4. Plug it in. Connect the pump to an electrical source, adjusting the water flow as desired. Use a flow restricter if needed. Conceal the ends of the board with mulch, rock, or spreading plants, making sure soil doesn't get inside the liner and muddy the water.
5. Care. Add water to the liner as needed. The pump will recirculate the water, but if water evaporates or runs off, it can burn out the pump. Remove the pump before the first freeze in the fall, then set it back in place each spring.