Why Your Faucet Drips and How to Diagnose the Cause

A faucet that drips once per second wastes more than 3,000 gallons of water a year, according to the EPA. That steady tick is also a clue. The pattern of the drip tells you which part wore out, and reading that pattern before you buy anything saves you from swapping the wrong piece and watching the drip come right back.

This guide is about finding the cause, not making the repair. By the end you should be able to point to a specific worn part inside one specific faucet. Once you know that, the hands-on fix lives in our guide on how to fix a dripping faucet (022), and a full cartridge swap has its own walkthrough (025). Here, you are a detective, not a mechanic. Three questions do most of the work: where does the water come out, which temperature side is failing, and does it drip only when the handle is off or only when it is running.

Spout Drip vs Handle Drip: What Each One Points To

Where the water shows up is the first thing to read, because it separates two different sealing jobs inside the faucet.

A drip from the end of the spout, while the handle is fully closed, means a seal that is supposed to hold back pressurized water has worn out. In a compression faucet (the older kind with separate hot and cold handles), that is almost always a hardened rubber seat washer or a pitted valve seat it presses against. In a single-handle cartridge, ball, or ceramic-disc faucet, a spout drip points to the cartridge itself or, on ball faucets, the small springs and rubber seats under the cap.

Water seeping from around the handle or pooling at the base of the faucet is a different failure. That is usually a worn O-ring, the round rubber ring that seals the moving stem or the spout where it meets the body. A handle that weeps only when you turn the water on, then stops when you shut it off, is the classic O-ring signature. This guide stays on spout drips. If your leak is actually at the base or handle, our guide on why a faucet leaks at the base or handle (026) owns that diagnosis, and a leak you trace to the supply line underneath belongs with our guide on sink sprayers and supply lines (195).

So before anything else, dry the whole fixture with a towel, run it, shut it off, and watch for sixty seconds. Note the exact spot the first new drop appears. That single observation rules half the suspects in or out.

Is It the Hot Side, the Cold Side, or Both?

Which temperature side drips tells you which internal seal failed, and on many faucets the two sides wear independently.

On a two-handle faucet, this is easy: close one handle completely and leave the other in normal use for a day, then switch. The side whose handle is shut when the spout drips is the failing side. Trade repair guidance notes that the hot side tends to wear first, because heat and thermal cycling are harder on rubber seals, though it is common to find both sides aging at a similar rate.

On a single-handle faucet you cannot isolate the sides by handle, but you can still gather a clue. Move the handle slowly through its full arc and notice whether the drip changes at the hot end, the cold end, or stays constant the whole way. A drip that worsens toward one extreme suggests wear on that side of the cartridge or its seats. A drip that holds steady no matter where the handle sits usually means the main sealing surface is gone, not one side of it.

Why bother with the hot/cold question if you are replacing the part anyway? Two reasons. It confirms the problem is inside the faucet and not, say, a supply issue feeding only one side. And on compression and ball faucets, the seats and springs are sold and replaced per side, so knowing which side failed tells you what to bring. Most repair sources recommend doing both sides at once on a compression faucet since the parts are cheap and the second side is rarely far behind, but that is a repair decision for guide 022, not a diagnosis you have to make here.

Matching the Drip to the Failing Part by Valve Type

The cause depends on the valve type, so identify the valve first, then read the drip against it. This is the heart of the diagnosis, and it is the step most “common causes of a dripping faucet” articles skip by just listing every possible part.

Start by naming the valve. Two separate handles almost always means a compression faucet with rubber seat washers. A single handle could be a cartridge, a ball, or a ceramic-disc valve. Our guide on how a faucet works (020) explains how to tell these apart by feel and teardown; this post assumes you can name yours.

Then match the symptom:

• Compression (two handles), drips from spout with handle off: worn rubber seat washer, or a corroded valve seat the washer can no longer seal against. If a new washer still drips, the seat is the cause.
• Cartridge (one handle), steady spout drip regardless of handle position: a worn cartridge that no longer seals the waterway. Cartridges fail as a unit and get replaced whole.
• Ball (one handle, often older kitchen faucets), spout drip: worn springs and rubber seats under the cap, or a worn ball.
• Ceramic-disc (one handle), spout drip: damage or mineral scoring on the disc cartridge or its inlet seals, often tied to debris or hard-water grit getting between the discs.
• Any type, weep at the handle or base: O-rings, not the spout-sealing part. That routes to guide 026.

Notice the pattern. A spout drip is a sealing-surface failure at the heart of the valve. A handle or base leak is an O-ring at the perimeter. Getting that distinction right is what stops you from buying a cartridge when you needed a fifty-cent O-ring, or scrubbing an aerator when the real problem is a worn seat.

Worn Washers, Seats, O-Rings, and Cartridges: How They Differ

Each part fails in its own way, so knowing what each one does makes the symptoms read like plain language instead of guesswork.

A seat washer is the soft rubber or composition disc at the end of a compression stem. Every time you close the handle, it is crushed against the metal valve seat to stop the flow. Over years that rubber hardens, cracks, or grooves, and water sneaks past as a spout drip.

A valve seat is the metal ring the washer presses into. Minerals and constant flow can corrode or pit it. A pitted seat is why a brand-new washer sometimes still drips: the sealing surface itself is no longer smooth, so nothing seats cleanly. This is a common reason a quick washer swap fails to hold.

An O-ring is a round rubber ring that seals a joint where parts move or meet, typically around the stem or where a spout swivels on its base. O-rings cause leaks at the handle or base, not at the spout. They harden and shrink with age and heat.

A cartridge is a self-contained valve, common in single-handle faucets, that controls both flow and temperature in one insert. It carries its own internal seals and O-rings. When the internal seal wears, you get a spout drip; when the external O-rings wear, you get a handle weep. Either way the usual answer is replacing the whole cartridge rather than rebuilding it.

The takeaway for diagnosis: spout drip points you toward washers, seats, ball springs, or the cartridge’s sealing core, while handle and base leaks point you toward O-rings. Matching the part to where the water appears is the whole job at this stage.

When the Drip Is the Faucet vs the Water Pressure Behind It

A worn part drips while the faucet is off; a pressure problem shows up only while the faucet is on, so use that on/off test to tell them apart.

Here is the cleanest single test in this guide. Wipe the faucet dry, shut the handle firmly, and watch.

• It keeps dripping with the handle off. This is a sealing failure inside the faucet, the worn washer, seat, cartridge, or ball-spring story above. The water is pushing past a seal that should hold.
• It only drips, sprays, or sputters while the water is running, then stops the moment you shut off. This is not a worn sealing part. Spitting or uneven flow while running usually traces to the aerator at the tip of the spout, which our guide on cleaning a faucet aerator (024) covers. Weak flow at this one faucet is its own diagnosis in our guide on why a single faucet has low water pressure (023).

High household water pressure can make a marginal seal drip sooner and faster, because more force is pushing on a worn part. But pressure does not create the drip on its own; a sound seal holds against normal household pressure. For context, standard faucets in the U.S. are built to deliver no more than 2.2 gallons per minute at 60 psi under federal rules, and WaterSense labeled bathroom faucets cap at 1.5 gallons per minute, so a faucet that suddenly drips is far more likely to have a worn part than to be facing more pressure than it was designed for. If you suspect the whole house runs high or harsh, that is a separate question handled in our pressure guides, not a faucet repair.

The why-it-matters here is simple math. EPA figures put the average household’s leaks at more than 9,300 gallons of water wasted a year, and they estimate that fixing easily corrected leaks can trim about 10 percent off a water bill. A drip you have correctly diagnosed is a drip you can stop on the first try.

Frequently Asked Questions

Does the side that drips tell me which part to buy?
On a two-handle faucet, yes. The handle you have shut when the spout still drips marks the failing side, and the seat washer or seats and springs for that side are what wore out. On a single-handle faucet you cannot isolate sides this way, so you identify the valve type and replace the cartridge or ball parts as a unit.

My faucet only drips when I turn it on, not when it is off. What does that mean?
That is usually not a worn sealing part. Sputtering or dripping only while running points to the aerator or to a flow issue at that fixture rather than a failed seal. A true worn-part drip continues after the handle is fully closed.

I replaced the washer and it still drips. Why?
The valve seat the washer presses against is probably corroded or pitted, so a smooth new washer still cannot seal against a rough surface. That is a seat problem, not a washer problem, and it is a common reason a quick swap does not hold.

Can high water pressure cause a faucet to drip?
High pressure can make an already worn seal drip sooner and harder, but it does not by itself make a healthy faucet drip. A sound seal holds against normal household pressure. If a faucet that never dripped suddenly does, suspect a worn part first.

Is a slow drip really worth fixing?
Yes. A faucet dripping once per second wastes more than 3,000 gallons a year by EPA’s count, and household leaks together average more than 9,300 gallons a year. The water and the bill add up faster than the drip suggests.

This article is general information, not professional advice; if water is reaching cabinets, walls, or floors, or you cannot isolate the source, have a licensed plumber take a look.

Sources

• EPA WaterSense, Fix a Leak Week: https://www.epa.gov/watersense/fix-leak-week
• EPA WaterSense, Bathroom Faucets: https://www.epa.gov/watersense/bathroom-faucets
• U.S. Department of Energy, Building Science Education, Low-Flow Fixtures (faucet flow rates): https://bsesc.energy.gov/energy-basics/low-flow-fixtures-bathroom-kitchen-faucets
• This Old House, How to Repair a Leaking Faucet (spout vs handle, seats and springs, O-rings): https://www.thisoldhouse.com/plumbing/how-to-repair-a-leaking-faucet
• Family Handyman, How to Fix a Leaky Faucet (washer, valve seat, cartridge, O-ring symptoms): https://www.familyhandyman.com/project/how-to-repair-a-kitchen-faucet/