Bathroom Faucet Plumbing: Types, Supply Lines, and How to Install One
Bathroom faucet plumbing comes down to three things: the faucet configuration your sink is drilled for, the flexible supply lines that feed it, and the mounting nuts that lock it to the deck. Get those right and a swap takes one to two hours. The three common setups are single-hole, 4 inch centerset, and 8 inch widespread, and they are not interchangeable, so the hole count and spacing decide what you can buy.
What are the bathroom faucet configurations?
Bathroom faucets come in three deck configurations tied to how the sink is drilled: single-hole, centerset with a 4 inch spread, and widespread with an 8 to 16 inch spread. Single-hole uses one drilling. Both centerset and widespread need three holes, but the distance between the outer holes differs, so measure center to center before buying.
Measure the spread from the center of the left hole to the center of the right hole. A 4 inch reading points to centerset. A reading of 8 inches or more points to widespread. Wall-mounted faucets skip deck holes entirely and rough into the wall, a job better planned during a remodel.
| Configuration | Holes | Spread (center to center) | Best for | Notes |
|---|---|---|---|---|
| Single-hole | 1 | N/A | Small vanities, modern baths, vessel sinks | Spout and handle in one body; a base plate can cover unused holes on a 3-hole sink |
| Centerset (4 in) | 3 | 4 in | Standard sinks, budget builds, rentals | Spout and two handles on one deck plate; the most common and usually the cheapest |
| Widespread (8 in) | 3 | 8 to 16 in | Larger vanities, traditional or high-end baths | Separate spout and handles connected below deck; more involved install |
Ordering a widespread for a sink drilled at 4 inches, or the reverse, means the faucet physically will not mount. This page covers the faucet and its hookups. For the drain, P-trap, and everything else below the basin, see the full under-sink assembly.
What supply lines does a bathroom faucet use?
Bathroom faucets connect to the two angle stop valves under the sink with flexible supply lines, typically 3/8 inch compression at the valve and a 1/2 inch FIP or faucet-specific connector at the tailpiece. Braided stainless steel lines in 20 inch or 30 inch lengths fit most vanities and resist kinking. You need two: one hot, one cold.
The 3/8 inch compression end threads onto the shutoff valve stem. The upper end either threads onto the faucet’s supply tubes or, on many one-piece faucets, comes as captive stainless tubing you connect directly. Bring your old lines to the store to match ends, since some faucets use a metric or brand-specific fitting rather than standard 1/2 inch FIP.
Angle stops (the small oval-handled shutoff valves) let you isolate the sink without killing water to the whole house. If a stop is stuck, corroded, or weeps when you turn it, replace the valve before finishing. That repair can involve compression or sweat fittings and, in many areas, is where DIY owners bring in a licensed plumber.
How do you install a bathroom faucet?
Installing a bathroom faucet means clearing the old unit, setting the new one on the deck, tightening the mounting nuts from below with a basin wrench, and connecting the supply lines to the shutoffs. Budget one to two hours. A basin wrench is the tool that makes it possible, since it reaches nuts your hand cannot.
- Shut off both angle stops under the sink. Open the faucet to relieve pressure and drain the lines. Put a bucket and towels below.
- Disconnect the supply lines at the valves with an adjustable wrench, then loosen the old faucet’s mounting nuts with a basin wrench and lift the faucet out. Scrape off old putty or gasket residue.
- Dry-fit the new faucet in the holes to confirm the configuration matches. Where the maker supplies no gasket, bed the base in plumber’s putty or run a thin silicone bead under the deck plate.
- Drop the faucet shanks through the holes. From below, hand-thread the mounting nuts, then snug them with a basin wrench. Stop a quarter turn past finger-tight; overtightening cracks porcelain or stone and strips shank threads.
- Connect the pop-up drain: feed the lift rod through the faucet, clip the clevis strap and spring clip to it, then seat the horizontal pivot rod in a clevis hole. Adjust so the stopper seals and lifts clear.
- Attach both supply lines. Wrap PTFE tape clockwise on any tapered male threads, hand-thread the nuts to avoid cross-threading, then give a gentle quarter turn past snug with the adjustable wrench.
- Open the angle stops slowly, run hot and cold for two to three minutes, and check every joint plus the drain connection for drips. Snug any weeping nut a hair more.
This is a faucet swap on existing lines. Replacing a whole kitchen faucet follows a similar order but with a deeper deck and a sprayer, covered in replacing a kitchen faucet. If your current faucet works but drips at the spout or handle, you may only need a cartridge or washer, so try fixing a dripping faucet instead before buying a replacement.
Why a basin wrench matters
A basin wrench is a long shaft with a spring-loaded pivoting jaw that grips mounting nuts and supply nuts in the cramped gap behind the basin. Clamp the jaw on the nut and turn the T-bar handle: counterclockwise to loosen, clockwise to tighten. It turns a job that is nearly impossible with pliers into a five-minute task.
How long does it take and does it need a permit?
A straightforward faucet swap on working shutoffs runs one to two hours for a first-timer. In most areas, replacing a faucet on existing supply and drain lines is minor repair that needs no permit. Moving or adding water lines usually does. Permit rules vary by state and city, so confirm with your local building department before opening a wall.
Frequently asked questions
What size are bathroom faucet supply lines?
Most bathroom faucet supply lines run 3/8 inch compression at the shutoff valve and either 1/2 inch FIP or a faucet-specific connector at the tailpiece. The 3/8 inch compression end threads onto the angle stop under the sink. Braided stainless lines in 20 inch and 30 inch lengths cover nearly every vanity, and they resist kinking better than old rigid risers.
What is the difference between a centerset and widespread faucet?
Both are 3-hole faucets, but the spread differs. A centerset mounts the spout and both handles on one base plate sized for holes 4 inches apart, center to center. A widespread splits the spout and two handles into separate pieces spanning 8 to 16 inches. They are not interchangeable, so measure your sink holes before you buy.
Can I install a bathroom faucet myself?
Yes, most homeowners install a bathroom faucet in one to two hours with a basin wrench, an adjustable wrench, and the new supply lines. Shut off the angle stops first, then work from below to reach the mounting nuts. Call a licensed plumber if the shutoff valves are seized, corroded, or leaking, since replacing an angle stop is a separate job.
Do you need plumber’s putty for a bathroom faucet?
It depends on the faucet. Many modern faucets ship with a rubber or foam gasket for the base and the drain flange, so no putty is needed. Where no gasket is supplied, a thin bead of plumber’s putty under the deck plate and pop-up drain flange seals out water. Skip putty on some plastic and stone surfaces the maker warns against, and use silicone there instead.
What tools do I need to install a bathroom faucet?
A basin wrench is the key tool, since it reaches the mounting nuts and supply nuts in the tight space behind the basin. Add an adjustable wrench, channel-lock pliers, a bucket and towels, plumber’s putty or silicone, and PTFE thread tape. A flashlight or headlamp helps under the vanity. Keep the faucet’s paper template if it shipped with one.
How do I connect the pop-up drain to the faucet?
The pop-up links the lift rod on the faucet to the drain stopper through a pivot rod and a slotted clevis strap. Feed the lift rod down through the faucet body, clip the spring clip and clevis to it, then connect the horizontal pivot rod into a hole on the clevis. Adjust the rod position until the stopper seats fully and lifts clear, then tighten the pivot nut.
Does a bathroom faucet need a permit?
In most areas, swapping a faucet on existing supply and drain lines is minor repair work that does not require a permit. Rules vary by state and city, and moving or adding water lines usually does trigger a permit. Check your local building department before any work that opens a wall or relocates plumbing, since code requirements differ by jurisdiction.
Last reviewed: September 2026.