Kitchen sink basin with the strainer and disposal opening in view
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Water Under the Kitchen Sink in Leander: What to Check

One of these two leaks runs all day. The other only shows when the water does. An hour and a paper towel tell you which one you have.

Sink RepairPublished September 22, 2026Vaquero Plumbing, RMP 15304

Water under a kitchen sink in Leander comes from one of two systems, and which one it is decides how fast you have to move. The supply side, meaning the shutoff valves and the flexible connectors feeding the faucet, is under pressure every minute of the day, so a leak there runs whether you are home or not. The drain side, meaning the strainer, the trap and the disposal, only leaks while water is going down it. Sorting one from the other takes about an hour and no tools, and it is the first thing we do on a sink call under licence RMP 15304.

Supply side or drain side: the test

Empty the cabinet, dry every pipe and fitting with a towel, and lay a sheet of paper towel across the cabinet floor. Then do not touch the sink for an hour.

If the paper is wet when you come back and nobody ran water, the leak is on the supply side. Turn both shutoff valves under the sink clockwise until they stop, which cuts the pressure to that faucet without shutting down the house, and get a plumber out. A supply leak has all day to work. The U.S. Environmental Protection Agency reports that nine percent of homes have leaks wasting 50 gallons or more per day, that the average household wastes more than 9,300 gallons a year to leaks, and that fixing the easy ones saves about 10 percent on a water bill.

If the paper stays dry until you fill the basin and pull the stopper, the leak is on the drain side. That is the better answer. A drain leak is not going to flood the kitchen overnight, and it usually comes down to a seal or a joint you can see.

Under the sink, part by part

These six parts are where we find it, and each one leaves a different signature.

  1. The shutoff valves. Also called angle stops. A slow weep at the packing nut behind the handle wets the valve body and then the cabinet floor under it. The valves that weep are usually the ones nobody has turned since the house was built.
  2. The flexible supply connectors. The braided lines from the valves up to the faucet. Water shows at the nut, at either end, and runs down the outside of the line, so the drip lands somewhere other than the failure.
  3. The faucet body and its deck seal. This one fools people. Water gets past a worn cartridge or around the base of the faucet, runs down the tailpieces inside the cabinet, and arrives looking exactly like a pipe leak. Dry the tailpieces, then run the faucet and the sprayer through every setting and watch where the first bead forms.
  4. The sink strainer. The basket that the drain bolts through. When its seal fails, the cabinet is dry all day and only gets wet when the basin holds standing water.
  5. The trap and its joints. The 2021 International Plumbing Code, which the City of Leander has adopted, allows slip joints only at the trap inlet, the trap outlet and within the trap seal, requires a liquid seal of 2 to 4 inches, caps the drop from the sink outlet to the trap weir at 24 inches with no more than 30 inches of horizontal run, and prohibits S traps outright. Under old sinks we still find S traps, extra slip joints added to make a mismatched kit reach, and flexible accordion tubing that catches food and holds water against every joint.
  6. The disposal and the dishwasher. A disposal leaks from the body seam or the drain elbow, and InterNACHI puts the life of a food waste disposal at 12 years. The dishwasher drain hose is the quiet one: the code says that hose has to rise and be fastened to the underside of the sink rim or countertop, and when it is lying flat instead, water works back and drips from the connection during a cycle.

Why these parts fail here

Hard water and high pressure are what shorten the life of a sink’s moving parts in Williamson County. The U.S. Geological Survey classes water above 180 milligrams per liter as calcium carbonate as very hard, and says that heated hard water forms scale that reduces the life of equipment, raises the cost of heating water, lowers the efficiency of electric water heaters and clogs pipes. Our own FAQ says the same thing in plainer words: Liberty Hill is known for hard water, and we constantly field calls about faucet clogs, broken water heaters and clogged drains that all trace back to water quality.

Pressure is the other half. The plumbing code Leander enforces requires a pressure-reducing valve wherever static pressure in a building exceeds 80 psi. Houses running above that line chew through faucet cartridges and supply connectors, and the sink is usually where it shows up first. InterNACHI gives a faucet and spray hose 15 to 20 years; scale and pressure take years off that. If the same faucet has been rebuilt twice already, replacement is the honest recommendation, and a slow drain in the same cabinet is worth looking at on the same visit.

The cabinet floor counts too

The EPA advises drying water-damaged areas and items within 24 to 48 hours to prevent mold growth, and says that where wet materials are dried inside that window, in most cases mold will not grow. It puts the limit for homeowner cleanup at about 10 square feet of mold, roughly a three foot by three foot patch, and says larger areas warrant a professional. Particleboard cabinet bottoms swell and stay damp, so pull everything out and put a fan on it while the repair is being arranged.

Who is allowed to do the work

Texas draws a clean line here. Section 1301.051 of the Occupations Code says a property owner is not required to be licensed to perform plumbing in their own homestead, so the law does not stop you tightening a slip nut under your own sink. Section 1301.351 says anyone who advertises or offers to perform plumbing must secure the services of a responsible master plumber, and that an unlicensed person may not engage in plumbing unless a licence holder supervises the work. A responsible master plumber carries $300,000 of general commercial liability insurance, pulls the permits and calls for inspections. Leander requires a permit for remodels involving plumbing and for water and wastewater connections, and tells homeowners to confirm the scope with a city building inspector.

Our own rule is shorter. Nothing that touches a gas line, a gas control valve or a flue, and nothing behind a wall or under a slab, is homeowner work or unlicensed work. That is licensed plumbing in Texas and we do it under RMP 15304.

Vaquero Plumbing repairs and replaces sinks, faucets, strainers, traps and shutoff valves across Leander and Liberty Hill, and our sink repair and installation page covers leak detection, clog removal and faucet work. The office is open Monday to Friday, 8:00 to 5:30, with Saturday by appointment. If the cabinet is filling while you read this, shut the valves, then call 512-893-8705 or use our emergency page.

Sources

  1. U.S. Environmental Protection Agency, WaterSense, Fix a Leak Week.
  2. U.S. Environmental Protection Agency, A Brief Guide to Mold, Moisture and Your Home and Mold Cleanup in Your Home.
  3. 2021 International Plumbing Code, Chapter 10, Traps, Section 409.4 and Section 604.8, ICC Digital Codes.
  4. City of Leander, Building Codes and Do I Need a Permit.
  5. Texas State Board of Plumbing Examiners, Plumbing License Law and Responsible Master Plumber.
  6. U.S. Geological Survey, Hardness of Water; InterNACHI, Standard estimated life expectancy chart for homes.

Questions Leander homeowners ask us

How do I know if the leak under my sink is urgent?

Dry everything under the cabinet, then leave the sink alone for an hour. If water comes back with nothing running, the leak is on the supply side and it is under pressure every minute of the day. Turn both shutoff valves under the sink clockwise until they stop, and call a plumber. If the cabinet stays dry until you fill and drain the basin, the leak is on the drain side, which is still worth fixing but will not flood the kitchen overnight.

Can I fix an under-sink leak myself in Texas?

Texas Occupations Code Section 1301.051 says a property owner is not required to be licensed to perform plumbing in their own homestead, so the law does not stop you working under your own sink. Anyone you hire is different: Section 1301.351 says a person who advertises or offers to perform plumbing must secure the services of a responsible master plumber. And nothing changes the rule on gas. Gas lines, gas control valves and flues are not homeowner work, and neither is anything behind a wall or under the slab.

The cabinet floor is swollen and dark. What now?

Dry it fast. The EPA advises drying water-damaged areas and items within 24 to 48 hours to prevent mold growth, and says that when wet materials are dried in that window, in most cases mold will not grow. Pull everything out, run a fan into the cabinet, and get the leak stopped in the same day rather than after the weekend. The EPA puts the do-it-yourself cleanup limit at about 10 square feet of mold, roughly a three foot by three foot patch.

Do you work on sinks outside Leander?

Yes. Vaquero Plumbing covers Liberty Hill, Leander, Cedar Park, Round Rock, Georgetown and Austin. The office is open Monday to Friday, 8:00 to 5:30, with Saturday by appointment.

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