Free Guide to Fixing a Leaking Sink

Understanding Common Sink Leak Types and Their Causes

A leaking sink is one of the most common household plumbing problems homeowners face. According to the U.S. Environmental Protection Agency, household leaks waste approximately 1 trillion gallons of water annually across the nation. A single dripping faucet can waste around 3,000 gallons per year—enough water to fill 180 bathtubs. Understanding where your leak originates is the first step toward fixing it yourself.

Sink leaks typically fall into several categories. Dripping faucets occur when internal washers or seals wear out over time. These are usually located under the handle and deteriorate from repeated use. Leaks under the sink happen when supply line connections loosen or when the P-trap (the curved pipe beneath the sink) develops cracks or corrosion. Leaks at the base of the faucet indicate that the seal around where the faucet connects to the sink has failed. Slow drains that back up with water also signal potential problems within the drain assembly.

The location of your leak determines which repair method you'll need. A leak at the faucet handle requires different tools than a leak at the base. Supply line leaks (the tubes bringing water to your sink) often need simple tightening or replacement. Drain leaks suggest issues with rubber gaskets or the P-trap assembly itself. Each leak type has distinct warning signs: puddles under the cabinet indicate drain or supply line issues, while water dripping from the faucet spout points to internal faucet problems.

Practical takeaway: Before starting any repair, locate your water shut-off valve under the sink and test it to ensure you can turn off water flow. Place towels or a bucket under the leak to catch water and better observe where water is actually coming from. Take clear photos of the leak from multiple angles—these will help you reference the problem while shopping for parts or consulting repair guides online.

Tools and Materials You'll Need

Most sink leak repairs can be completed with tools you likely already own or can borrow. The basic toolkit includes an adjustable wrench (useful for tightening connections and removing faucet nuts), slip-joint pliers (also called tongue-and-groove pliers, perfect for gripping pipes without slipping), and a standard screwdriver set with both flathead and Phillips head options. A flashlight or headlamp becomes invaluable when working under the sink where visibility is poor. Many people find that a small bucket or shallow pan catches water during disassembly, preventing water from spreading across your cabinet floor.

Specific parts you might need depend on your leak type. Faucet washers (small rubber or plastic discs, typically costing $2-5) fix most dripping faucets—they come in various sizes, so knowing your faucet's brand and model helps. O-rings (rubber seals available in multiple sizes from hardware stores for $1-3 per package) stop leaks at connection points. Plumber's tape (also called thread seal tape or Teflon tape, around $3-5 per roll) wraps around threaded connections to create watertight seals. For more significant issues, you might need a P-trap replacement kit ($15-40) or new supply line hoses ($10-30 each).

Before purchasing parts, determine your faucet type. Older homes often have compression faucets with two separate handles—these use washers. Modern single-handle faucets may use cartridges or ball mechanisms. Look under your sink for the faucet brand name and model number, often stamped on the faucet body. This information helps you purchase the exact replacement parts needed. Many hardware stores provide free identification services if you bring in photos or the faucet model number.

Practical takeaway: Visit your local hardware store with photos of your leak and faucet. Store employees often provide free guidance on which tools and parts match your situation. Buy slightly more plumber's tape and washers than you think you'll need—they store indefinitely and are inexpensive. Keep all receipts in case you need to exchange parts, and ask store staff if they offer returns on unused plumbing supplies.

Step-by-Step Repair Process for Faucet Drips

Fixing a dripping compression faucet (the most common type in older homes) follows a logical sequence. Start by turning off the water supply under the sink using the shut-off valve. Turn on the faucet to release remaining water pressure in the lines. Use your screwdriver to remove the decorative cap or handle screw to access the packing nut—this is typically a hex-shaped nut directly under the handle. Once you locate it, use your adjustable wrench to turn the packing nut counterclockwise and remove it completely.

With the packing nut removed, pull the stem (the vertical piece that moves up and down with the handle) straight up and out. You'll see a washer at the base of the stem held in place by a brass screw. This washer is usually the culprit behind your drip. Unscrew the brass screw using your screwdriver and remove the old washer. Bring this washer to your hardware store to match the size, or measure its diameter (common sizes include 3/8-inch and 1/2-inch). Install the new washer, reinstall the brass screw firmly, and reverse the process by sliding the stem back in and tightening the packing nut.

For single-handle faucets, the process differs slightly. You'll need to remove a small set screw (usually hidden under a decorative cap) that holds the handle in place. Once removed, the handle lifts away, exposing the cartridge or ball assembly. Cartridge faucets require a special removal tool (typically $5-15 at hardware stores). Before starting, take photos showing the cartridge orientation so you can reinstall it correctly. Pull the cartridge straight out—don't twist it. Order a replacement cartridge matching your faucet brand and model, install it in reverse, and your faucet should stop dripping.

Practical takeaway: Work slowly and methodically, taking photos at each step before removing pieces. Keep all small parts in a clean container so you don't lose them down the drain. If water continues dripping after washer replacement, the issue may be valve seat corrosion (the stationary part the washer seats against). This requires a valve seat wrench (around $10-20) and a replacement valve seat, or potentially a professional plumber's help.

Fixing Leaks Under the Sink and Supply Line Issues

Leaks originating under the sink often stem from loose connections or damaged supply lines. First, turn off the water supply valve. Inspect the two flexible metal hoses connecting the shut-off valves to the faucet's hot and cold water inlets. These supply lines sometimes develop pinhole leaks or fail at connection points. If you see water dripping from where a supply line connects to the shut-off valve or faucet, try tightening that connection using your adjustable wrench. Grasp the connector nut with one wrench while turning the valve connection with another wrench, turning clockwise to tighten. A quarter-turn often stops minor leaks.

If tightening doesn't stop the leak, you'll need to replace that supply line. Turn off the water, place a bucket underneath, and unscrew the old supply line from both ends (the shut-off valve and faucet inlet). Take it to your hardware store to match the length and connection sizes. Most supply lines come in 12, 16, 20, or 24-inch lengths with 3/8-inch or 1/2-inch connections. Install the new supply line by hand-tightening it at both ends first, then using your wrench to tighten each connection an additional quarter-turn. Hand-tight connections are often sufficient for supply lines.

P-trap leaks appear as water dripping from the curved pipe directly under the sink. Place a bucket underneath and loosen the slip nuts (the large threaded connectors) at both ends of the P-trap using your slip-joint pliers. The trap will drain into your bucket. Inspect the rubber washers inside each slip nut—if they're hardened, cracked, or deteriorated, replace them. If the P-trap itself is cracked or severely corroded, you'll need to replace the entire assembly. Replacement P-traps cost $15-40 and come in various materials (PVC plastic, chrome-pl