What You'll Do: Turn Off Water, Remove the Old Faucet, Install the New One, and Test

Replacing a bathroom sink faucet takes about an hour if you have the right tools and the shutoff valves under your sink work. You'll turn off the water supply, disconnect the old faucet from the supply lines, remove it from the sink, set the new faucet in place, reconnect the lines, and turn the water back on. Most homeowners can do this without calling a plumber—the hardest part is usually reaching the bolts underneath the sink, not the actual plumbing.

The job requires only basic tools: an adjustable wrench, a screwdriver (usually flathead), and possibly a basin wrench if the space under your sink is tight. You'll also need the new faucet itself, which comes with mounting hardware and instructions specific to that model. Read those instructions before you start, because faucet designs vary—some mount from above the sink, others from below, and the connection method changes the order of your steps.

Key Takeaways

  • Turn off the water at the shutoff valves under the sink first, then open the faucet to release pressure before you disconnect anything.
  • The old faucet is held down by bolts underneath the sink; you'll need to reach under and loosen them with a wrench, then pull the faucet up through the sink hole from above.
  • Clean the sink surface where the old faucet sat before you install the new one, because old caulk or mineral deposits can prevent a watertight seal.
  • Connect the hot and cold supply lines to the correct ports on the new faucet—hot on the left side, cold on the right—and hand-tighten the connections before using a wrench.
  • Turn the water back on slowly and check for leaks at every connection point before you consider the job finished.

Gather Your Tools and Materials Before You Start

You need an adjustable wrench (8 to 10 inches long), a flathead screwdriver, a bucket or towel to catch water, and the new faucet with its hardware. Check under your sink before you buy the faucet: measure the distance from the center of one hole to the center of the next. Most bathroom faucets are 4 inches or 8 inches apart. The faucet box will tell you what spacing it fits.

If the space under your sink is very tight, a basin wrench—a specialized tool with a long handle and a small head that grips nuts from the side—makes reaching the mounting bolts much easier. You can rent one from a hardware store for a few dollars if you don't own one. Have your new faucet's instruction sheet ready; different models connect differently, and the manufacturer's steps take priority over general instructions.

Turn Off Water and Disconnect the Supply Lines

Look under the sink. You'll see two shutoff valves—one for hot water, one for cold—connected to the supply lines that feed the faucet. Turn both valves clockwise until they stop. They should turn easily; if one is stuck or won't turn, you may need to shut off water to the whole house instead (usually at the main valve near your water meter or where the line enters your home).

Open the faucet at the sink to release any pressure in the lines. Water may drip out, which is normal. Place a bucket or towel under the supply lines, then use your wrench to loosen the nuts where the supply lines connect to the faucet. Turn counterclockwise. Once loose enough to turn by hand, unscrew them the rest of the way and set them aside. If water drips, that's expected—the bucket catches it.

Remove the Old Faucet from the Sink

Reach under the sink and locate the mounting bolts that hold the faucet to the sink from below. Most faucets have two bolts, one on each side. Use your wrench to loosen them by turning counterclockwise. You may need to hold the nut on top of the bolt with one wrench while turning the bolt underneath with another, or use a basin wrench if space is tight. Loosen both bolts until they come free.

Go back to the top of the sink and pull the old faucet straight up and out. It may resist slightly if old caulk is holding it down; a gentle rocking motion usually frees it. Once it's out, clean the sink surface thoroughly with a damp cloth. Scrape away any old caulk, mineral deposits, or corrosion with a flathead screwdriver. A clean surface ensures the new faucet will seal properly and sit flush against the sink.

Install the New Faucet and Reconnect Water Lines

Read your new faucet's instructions—the exact steps depend on the design. Most faucets come with a rubber gasket or mounting ring that goes on the underside of the faucet. Place the faucet into the sink holes from above, making sure it sits straight and centered. From underneath, slide the mounting hardware (gasket, washers, and bolts) onto the faucet's threaded posts, then hand-tighten the bolts. Once hand-tight, use your wrench to tighten them further, but do not over-tighten—you want the faucet snug, not crushed.

Now reconnect the supply lines. The hot water line (usually marked red or left) connects to the hot port on the faucet; the cold water line (usually marked blue or right) connects to the cold port. Hand-tighten the connection nuts first, then use your wrench to snug them. They should be tight enough that water won't leak, but you don't need to force them—hand-tight plus a quarter turn with the wrench is usually right.

Turn Water Back On and Check for Leaks

Turn both shutoff valves counterclockwise slowly. Open the faucet and let water run for 10 to 15 seconds to flush out any debris from the lines. Then turn the faucet off and watch underneath the sink for drips. Check every connection point: where the supply lines meet the faucet, where the faucet bolts go through the sink, and where the supply lines connect to the shutoff valves. A small drip at a connection usually means the nut needs another quarter turn with your wrench.

If water drips from under the faucet itself (between the faucet and the sink), the gasket may not be seated properly. Turn off the water, remove the faucet, clean the sink surface again, and reinstall it. If you see water coming from the shutoff valves themselves, those valves may be worn out and need replacement—that's a separate job, but the good news is your new faucet is now installed correctly. Let the water run hot and cold a few times to make sure both sides work, then you're done.

Common Mistakes to Avoid

The most common mistake is forgetting to turn off the water before disconnecting the supply lines. Water will spray everywhere, and you'll have a mess. The second is over-tightening the mounting bolts, which can crack the sink or strip the threads. Hand-tight plus a small wrench turn is enough. Third is connecting the hot and cold lines backward—it won't break anything, but your faucet handles will work opposite to what you expect.

Another frequent problem is not cleaning the old caulk and mineral deposits from the sink before installing the new faucet. This prevents a watertight seal and causes leaks around the base. Finally, some people rush the supply line connections and don't tighten them enough. The connection should be snug—if you can turn the nut by hand after the wrench is done, it's not tight enough. A small leak at a connection is a sign to tighten it a bit more.

Frequently Asked Questions

What if the shutoff valves under my sink don't work?

If a valve won't turn or water still flows after you turn it, you'll need to shut off water to the whole house. Find your main water shutoff valve (usually near the water meter or where the line enters your home) and turn it clockwise. Once the main is off, the shutoff valves under the sink are no longer needed for this job. After you finish installing the new faucet, consider having a plumber replace those old valves so they work next time.

Can I install a new faucet if my sink has only two holes but the new faucet needs three?

No, the faucet must fit your sink's hole pattern. Before you buy, measure the distance between holes and count how many you have. If your sink has two holes and the faucet needs three, you'll need a different faucet or a different sink. Some faucets come with a cover plate that hides extra holes, but that only works if the faucet needs fewer holes than your sink has.

Do I need to use plumber's tape on the supply line connections?

Most modern faucets and supply lines use compression fittings that don't need tape—the nut and ferrule create the seal. Check your faucet's instructions. If it calls for tape, wrap it clockwise around the threaded part three times before connecting. If the instructions don't mention tape, you don't need it.

How tight should the supply line nuts be?

Hand-tighten first, then use a wrench to turn another quarter to half turn. The goal is snug enough to stop leaks, not so tight that you strip the threads or crack the fitting. If you turn the wrench and feel strong resistance, stop—you're tight enough. A small leak at the connection means you need another quarter turn, not a full rotation.

What if water leaks from under the faucet after I install it?

The gasket or mounting ring isn't sealing properly. Turn off the water, loosen the mounting bolts, and lift the faucet out. Clean the sink surface again with a damp cloth and scrape away any debris. Reinstall the faucet, making sure the gasket sits flat and centered, then retighten the bolts. If it still leaks, the gasket may be damaged and need replacement—check if your faucet came with a spare or contact the manufacturer.