Attach the two 16-inch diameter terra cotta pots together base to base with waterproof construction adhesive. Allow the adhesive to dry. This is the stand for the tiers on the outdoor water fountain.
Place a submersible fountain pump inside the upright 16-inch diameter terra cotta pot. This pot is the reservoir for the water fountain. Feed the electrical cord from the pump through the drainage holes in the two joined pots. Use silicone sealant to close the opening around the cord so that the terra cotta pot is water tight. Let the sealant dry.
Cut a 55-inch length of plastic tubing. Attach one end of the plastic tube to the spout on the pump. Fill the terra cotta pot with water.
Drill 3/4-inch holes in the center of each terra cotta saucer. Make sure that you use a ceramic drill bit. Drill a 3/4-inch hole on either side of the rim of the 12-inch diameter pot. The holes will allow water to flow from the saucer back into the 16-inch reservoir.
Place the 18-inch diameter saucer on top of the 16-inch diameter pot, feeding the plastic through the drilled center hole. Do not glue the saucer to the rim of the pot, as you will need to move it periodically to add water. The weight of the remaining tiers will hold the saucer in place.
Place the 12-inch diameter terra cotta pot upside down over the center of the 18-inch saucer. Feed plastic tubing through the pot's center drainage hole. Glue the rim of the pot to the saucer with waterproof construction adhesive.
Center the 14-inch saucer on top of the upside down terra cotta pot while feeding the plastic tube through the drilled hole. Seal the hole around the tubing with silicone sealant. Glue the saucer to the pot.
Center the 10-inch terra cotta pot on top of the 14-inch saucer while feeding the plastic tube through the drainage hole. You can invert the 10-inch pot or leave it right side up. Seal the opening around the plastic tubing with silicone. Glue the pot to the saucer with waterproof construction adhesive.
Center the 12-inch diameter saucer on top of the 10-inch pot while feeding the plastic tube through the hole. Seal the opening around the tube with silicone. Glue the saucer to the pot.
Center the 8-inch diameter pot on top of the 12-inch diameter saucer. Feed the plastic tube through the hole--and then seal the hole. Glue the pot to the saucer.
Feed the plastic tubing through the drilled hole in the 10-inch diameter terra cotta saucer as you center it onto the 8-inch diameter pot. Seal around the hole; and then glue the saucer to the pot.
Fill each tier with water before turning on the fountain pump. The water will circulate from the 16-inch diameter pot to the 10-inch diameter saucer at the top of the tier. The water will flow over the successively larger tiers and back down into the reservoir.