Cut the two 6-inch-by-6-inch wood posts equal to the desired height of your curtain waterfall plus 18 inches. Cut the 2-inch-by-4-inch plank equal to the desired width of your curtain waterfall, plus 12 inches.
Dig two 18-inch-deep holes where you plan to place the side beams for your curtain waterfall. Line the bottom of the holes with gravel. Stand the side beams into the holes and brace them with wood planks.
Mix the mortar and fill the holes around the beams to ground level. Allow the mortar to dry. Remove the plank braces.
Attach the 2-inch-by-4-inch planks across the top of the two side beams with metal L brackets. Place one plank on the front of the beams and one plank on the back.
Place a rectangular concrete planter between the two posts. This is the reservoir for your waterfall.
Cut one section of PVC pipe to fit the height of your side beams, less the height of your planter. Cut one section of PVC pipe to fit the width of your curtain waterfall, plus 3 inches.
Attach the PVC end cap to one end of the width pipe with PVC cement. Connect the open end of the width pipe to one end of the height pipe with a PVC elbow.
Attach the PVC height pipe to the back side of one of the side beams with flexible metal U brackets. Attach the PVC pipe across the plank at the back of the wood structure with U brackets on either end.
Drill holes in the bottom of the PVC pipe that runs across the wooden structure. Make sure that the holes fall within the sides of the concrete planter.
Place the waterfall pump inside the planter. Run a length of plastic tubing from the water spout on the waterfall pump to at least 2 feet inside the PVC pipe on the back of the wooden structure.
Fill the planter with water and turn on the waterfall pump.