The Delta single lever waterfall faucet has a gooseneck spout that arches over the sink. This part includes a simple aerator and O-ring seal at the base. If the faucet spout is leaking or operating poorly, replacing the O-ring is your best bet to fix the problem. Most leaks in the spout originate here; therefore, installing a brand new ring will usually correct the issue.
Turn off the water by closing both valves on the pipes leading to the faucet. Each is located under the sink. Turn on the faucet to drain remaining water from pipes.
Disconnect the quick connect hose underneath the sink by pulling it down and out of the connection. This is the plastic hose connecting the spout to the water line.
Remove the nut attaching the faucet to the sink by loosening the washer with a pair of pliers or a hexagonal wrench. Pull the spout out of the sink and place it on a flat surface.
Remove the spout bonnet, which is the metal sleeve at the bottom of the faucet, and the spout retainer that holds the spout in place. Remove the O-rings on top of and below the base of the spout. You must also remove the washer, if it still remains in place. Replace the old O-rings with new ones.
Reassemble the spout by sliding the retainer and bonnet back on the spout. Connect the spout to the sink by sliding it into the sink's spout hole. Slide the washer over the bottom of the spout O-ring assembly under the sink, and tighten the nut under the sink with pliers. Reconnect the quick connect hose. Turn on the water to test the faucet.