How to Install a Bathroom Sink Faucet

Installing a bathroom faucet is one of the most satisfying plumbing upgrades you can do yourself—it transforms the sink in an afternoon and costs far less than hiring a plumber. A new faucet is also one of the first things you notice every morning, so it's worth doing right. The difference between a professional-looking installation and a leaky mess is attention to the mounting hardware, proper thread sealing, and taking time to check for leaks before you call it done. Whether you're replacing a worn-out single-handle model or upgrading to a modern double-handle faucet, the core steps are the same: remove the old one, prepare the sink holes, secure the new faucet, and connect the water supply lines.

1. Shut Off Water First. Locate the shutoff valves under the sink—usually two small knobs below the basin. Turn both the hot and cold valves clockwise until they're fully closed. If you can't find them or they don't work, shut off the main water supply at the meter or pump. Open the faucet at the sink to release any remaining water pressure in the lines.
2. Unscrew Both Supply Lines. Place a bucket under the sink to catch residual water. Using an adjustable wrench, hold the coupling nut on the supply line where it meets the faucet (or shutoff valve) and turn counterclockwise. Once loose, unscrew by hand. Repeat for both hot and cold lines. If the coupling is stuck, apply penetrating oil and wait 10 minutes before trying again.
3. Loosen Mounting Nuts Below. From underneath the sink, locate the mounting nuts that secure the faucet to the sink deck. These are usually large hex nuts on the threaded studs that come down from the faucet body. Using an adjustable wrench or basin wrench (a specialized tool with a long shaft), turn these nuts counterclockwise and remove them. You may need to have someone hold the faucet from above to prevent it from spinning. Lift the old faucet out of the sink.
4. Clean the Mounting Surface. Use a soft cloth and mild abrasive (like Bar Keeper's Friend or a non-scratch scrub pad) to remove old sealant, mineral deposits, and corrosion from the sink holes and surrounding deck. Wipe clean with a damp cloth and dry thoroughly. This ensures a watertight seal for the new faucet.
5. Lay Out All Components. Before installing the new faucet, lay it out on the counter and identify all components: the faucet body, mounting hardware kit (usually includes rubber washers, gaskets, and nuts), supply lines (sometimes pre-attached, sometimes loose), and any aerator or deck plate. Follow the manufacturer's diagram to assemble the faucet body if it's a two-handle model with separate handles and spout. Insert the mounting studs through the gasket and washer in the order specified by the instructions.
6. Secure the Faucet Body. Carefully lower the faucet assembly into the sink holes, aligning the mounting studs with the pre-drilled holes in the sink deck. The mounting gasket or rubber seal should sit flat against the sink surface. From underneath the sink, thread the washers and mounting nuts onto the studs. Start all three nuts by hand to ensure they're going on straight, then use a basin wrench or adjustable wrench to tighten them in a star pattern (tighten one, skip one, tighten one, return to the first). Tighten snugly but not aggressively—you're aiming for a secure seal, not crushing the gasket.
7. Connect Supply Lines Properly. You now have three options depending on what came with your faucet: pre-attached braided supply lines (most common), loose lines you need to attach to the faucet inlet ports, or lines that need to be connected to the shutoff valves. If lines aren't pre-attached, screw them onto the faucet inlet ports hand-tight, then use a wrench to tighten an additional quarter-turn. Connect the other end of the hot line to the hot shutoff valve and the cold line to the cold shutoff valve, again hand-tight plus a quarter-turn. Wrap the connection point with one layer of plumber's tape (also called thread seal tape or PTFE tape) before screwing on the coupling nut to ensure a watertight seal.
8. Watch for Drips Carefully. Slowly turn on both shutoff valves by turning the handles counterclockwise. As pressure builds, watch carefully for drips or streams of water at every connection point you made: the supply line couplings at the faucet, the couplings at the shutoff valves, and the mounting gasket at the sink deck. Turn on the faucet and run water for 30 seconds, checking again for leaks. Do not move on until you see zero drips.
9. Seal Any Leaking Threads. If you see a slow drip at a coupling nut, place a bucket underneath it and use an adjustable wrench to tighten that nut another quarter-turn. Wait 30 seconds and recheck. If the drip continues, turn off the water, unscrew the nut completely, wrap the male fitting thread with an additional layer or two of plumber's tape, and reconnect. For leaks at the mounting gasket under the sink, turn off the water and re-tighten the mounting nuts in a star pattern—often one side has settled slightly during installation.
10. Verify Hot and Cold Flow. Run water with the handle in the full hot position for 10 seconds, then full cold position for 10 seconds, then the mixed center position. Feel for any vibration or unusual sounds (which might indicate debris in the lines or an air lock). Check that water flows smoothly at all temperatures and that the handle moves freely. If you notice weak flow, the aerator (the screen at the faucet outlet) may be partially clogged from installation debris—unscrew it by hand, rinse it under water, and screw it back on.
11. Cover Holes with Deck Plate. Some faucets come with a decorative deck plate or trim ring that covers the holes in the sink and the gap between the faucet and the sink surface. Position this around the base of the faucet from above and secure it according to the manufacturer's instructions—usually either with clips underneath or with caulk. If using caulk, apply a thin bead of 100% silicone caulk around the perimeter of the deck plate where it meets the sink, smooth it with a wet finger, and let it cure for 24 hours before using the sink.
12. Inspect Everything One Last Time. After the caulk has cured (or immediately if there's no caulk), run the faucet again and perform a final inspection under the sink with a flashlight. Look for any moisture on the shutoff valves, on the cabinet bottom, or dripping into the bucket. Wipe away any dust or water from the installation. Remove the bucket and check the cabinet floor underneath. If everything is dry and the faucet operates smoothly, the installation is complete.