12 Signs It's Time to Call for Professional Leak Detection

Water leaks seem minor at first, but left alone they quietly damage walls, floors and foundations, feed mold and push up water bills long before anyone sees a puddle. In San Jose and South Bay homes, slab foundations, aging galvanized pipe and underground irrigation lines are where leaks most often hide.

Each kind of leak has its own warning signs, and catching them early keeps the repair small.

Professional leak detection uses thermal imaging, acoustic listening equipment, moisture meters and pressure tests to find the leak without tearing into the house. Regular checks are worth it for older homes and homes with high water use. These are the 12 signs that it’s time to call for leak detection.

If you’d like to test for a leak yourself first, see how to detect water leaks in your home for the whole-house check, or how to detect pipe leaks for step-by-step tests of the pipes and the underground service line.

Common Signs of Household Leaks

Household leaks usually develop out of sight: behind walls, under floors or above ceilings. By the time the damage shows, water may have been soaking into drywall, insulation and framing for weeks. Watch for stains, mold, damp flooring, a drop in water pressure, and a meter or bill that tells you water is going somewhere.

1. Water Stains on Ceilings and Walls

Yellow or brown patches on a ceiling or wall are left behind as water from a leaking pipe soaks through the building materials. The stain usually spreads outward and darkens as the leak continues. Left alone, it weakens the drywall, can cause sagging or bubbling paint, and leads to mold. A stain under a bathroom or below a second-floor laundry is a common sign of a leaking supply line, drain or shower pan. Have it checked even if the stain looks dry; slow leaks come and go with use.

2. Mold Growth Around Pipes

Mold grows wherever moisture stays, and a slow leak is a steady supply. It often goes unnoticed under sinks, inside vanity cabinets, behind the washing machine or along baseboards. Besides damaging walls and insulation, mold can trigger allergic reactions and breathing problems, especially for people with asthma. Cleaning the mold isn’t enough: the leak feeding it has to be found and fixed first. The EPA advises fixing plumbing leaks and other water problems as soon as possible and drying everything completely.

3. Wet Carpet Near Plumbing Fixtures

Damp carpet or flooring around a sink, toilet, tub, washing machine or water heater means water is escaping nearby. Common sources are a loose supply connection, a worn toilet wax ring, a cracked washing machine hose or a corroded fitting. Check under the fixture and behind the appliance; tighten a loose compression nut or replace a worn hose if you’re comfortable doing it. If the floor stays damp, the leak is in the wall or under the floor, and it needs a plumber before the subfloor rots or mold sets in.

4. Low Water Pressure

A leak lets water escape before it reaches the faucet, so a drop in pressure, especially throughout the house, can point to a leak in a supply line. Before you call, rule out the simple causes: a clogged faucet aerator or showerhead, or a partly closed shutoff or main valve. If pressure stays low, look for damp spots and stains and listen for running water with the taps off. In older South Bay homes, low pressure everywhere is also a classic sign of corroded galvanized pipe; see how repiping improves water pressure.

5. Musty Odor in Damp Areas

A musty, earthy smell in a closet, a cabinet, a crawl space or a room that shares a wall with a bathroom usually means mold or mildew is growing on hidden moisture. Poorly ventilated spaces near plumbing are the most common places. Ignoring the smell lets the damage spread. Find and fix the leak first, then deal with the mold; large areas of mold, or mold after a lot of water damage, call for a mold remediation professional.

6. Cracked or Warped Walls and Floors

Moisture building up behind a surface makes wood floors cup or buckle, tile loosen, baseboards swell and drywall bulge or go soft. Press gently on drywall near plumbing walls and look for cracks, soft spots and warped boards near fixtures and pipes. Over time this damage affects more than looks: wet framing and subfloors lose strength. A plumber can find the source so the repair doesn’t just cover up a leak that’s still running.

7. A Water Meter That Moves When Nothing Is On

Your water meter is the simplest leak test there is. The EPA’s WaterSense program suggests you check your meter before and after a two-hour period when no water is being used; if the reading changes at all, you probably have a leak. Turn off every faucet and water-using appliance (and the irrigation timer) before you start. A water bill that climbs with no change in how you use water is the same warning in slower form.

The most common hidden leak is a toilet. To test one, put a few drops of food coloring in the tank and wait; the EPA says that if color shows up in the bowl after 10 minutes, the toilet is leaking (usually a worn flapper). Flush afterward so the color doesn’t stain the tank.

8. Warm Floors or the Sound of Running Water

A warm spot on a tile or concrete floor is a common sign of a hot water line leaking under a slab foundation. The sound of running or hissing water inside a wall or under the floor when nothing is on is another. Neither leak shows any water until the damage is well along, and both need professional equipment to locate. See slab leak signs.

Common Signs of Sewer or Drain Leaks

Sewer and drain leaks come from tree roots, aging and cracked pipe, and blockages that put the line under pressure. Left unchecked, they soak the soil, spread bacteria, can damage foundations and release sewer gas, so they’re a health problem as well as a plumbing one. Besides the two signs below, watch for slow drains, frequent backups and gurgling toilets or drains. Call a plumber at the first sign of a sewer problem; these leaks get worse quickly.

9. Unpleasant Odors from Drains

A foul smell from one drain is often trapped food, hair or a dry P-trap (run water in a guest bath or floor drain that hasn’t been used). A sewage smell that keeps coming back, or one you notice in several rooms, the crawl space or the yard, can mean a cracked drain or a leaking sewer line releasing sewer gas. Sewer gas is unpleasant and unhealthy to breathe, and in high concentrations it can be dangerous: air out the house and have a licensed plumber inspect the drain system rather than trying to open lines yourself.

10. Wet Yard Spots from Underground Leaks

Soggy ground, puddles, mud or an unusually green strip of lawn that isn’t explained by rain or watering often sits right above a buried pipe. It can be the sewer lateral, a drain line or the water service line from the meter. The extra moisture damages landscaping and, close to the house, can affect the foundation. A sewer camera inspection shows cracks, breaks and root intrusion in the sewer line, and leak detection locates a leaking water line.

Signs of Irrigation Leaks

Irrigation leaks are common in lawns and gardens because the lines and valves are underground, and leaks at connection points can go unnoticed for months. They waste water, water some areas unevenly and damage the landscape, and in summer they show up mostly as a higher bill. Look for waterlogged or unusually green patches, broken or misaligned sprinkler heads, pooling water and uneven coverage. Visual checks each spring and after any digging catch most problems early.

11. Broken, Cracked or Leaking Sprinkler Heads

A damaged sprinkler head throws off the watering pattern, so some areas get too much water and others dry out, and a broken head can gush water every time the zone runs. Run each zone and look for cracks, heads that are tilted or stuck, weak or misdirected spray, and water pooling around a head or a valve box. Pooling usually means a broken head or a cracked pipe below it. Damaged heads should be replaced promptly; pooling near the house should be fixed quickly so it doesn’t soak the foundation.

12. Soggy Grass, Uneven Coverage or Weak Spray

Constantly waterlogged grass can mean a leak in a buried line or valve rather than overwatering. It leads to root rot and fungus and draws mosquitoes and gnats. Uneven coverage, with stressed grass in some spots and soggy ground in others, can come from clogged nozzles or misaligned heads, but also from a leak lowering pressure in that zone. A drop in pressure while the sprinklers run, with weak spray patterns, points to a clogged nozzle, a damaged pipe or a leak. Clean nozzles and adjust the heads first; if the problem stays, have the line checked for a leak. Adjust the watering schedule to the weather in the meantime.

General Leak Detection Tools

Professional leak detection finds hidden leaks early without opening walls, floors or the yard on a guess. Each tool has its own job: thermal cameras see the temperature difference that moisture or a hot water leak makes, acoustic equipment hears water escaping from a pressurized pipe, and pressure tests confirm whether a line is leaking at all. Used together, they narrow the leak down to a small area, so the repair needs only a small opening.

Infrared Detection for Temperature Variations

Thermal imaging cameras show temperature differences across walls, floors and ceilings. Wet materials usually read cooler, and a hot water leak reads warmer, so a camera can trace a leak behind drywall or under a floor without cutting into it. It saves time and avoids exploratory demolition, and it’s often the first tool used to follow a slab leak.

Acoustic Detection for Water Flow Sounds

Acoustic leak detectors use sensitive ground and contact microphones to pick up the sound of water escaping from a pressurized pipe. They work where nothing is visible: under a slab, underground in the yard or inside a wall. The technician follows the sound to where it’s loudest to mark the exact spot for a targeted repair.

Leak Detection Methods Compared

Pressure testing of gas lines is a job for a licensed plumber only. For what a visit costs, see leak detection cost, and for the methods in more depth, how to detect water leaks.

What Should You Do If You Find a Leak?

Act quickly: the longer water runs, the more damage, mold and cost. Stop the water, get a plumber to find and fix the source, record the damage for your insurer and protect your belongings while you wait. Once the leak is fixed, regular inspections help catch the next one early.

Turn Off the Water Supply

For a leak at one fixture, such as under a sink or behind a toilet, close that fixture’s shutoff valve. For a leak you can’t isolate, or any active damage, close the main shutoff, usually where the water line enters the house or near the meter. Stopping the flow limits the damage and makes it easier for the plumber to find the leak. Learn where your main shutoff is before you need it.

Contact a Professional Plumber

Call a licensed plumber who does leak detection and repair to find the source, fix it properly and check for related damage. In San Jose, finding a typical accessible leak usually costs $150 to $600; hard-to-find leaks under slabs or underground can run up to about $1,500. Repeated leaks in old pipe may mean it’s time to repipe.

Document the Damage for Insurance

Take photos and video of every affected area (walls, floors, ceilings, cabinets and damaged belongings) before cleanup, and keep the plumber’s invoice and notes on the cause. Policies vary: many cover sudden water damage and sometimes the cost of finding the leak, but not gradual leaks or replacing worn pipe. Call your insurer early and keep records of everything you spend.

Prevent Future Leaks Through Regular Inspections

Routine checks catch worn supply hoses, corroded fittings, leaking valves and irrigation problems before they cause damage. Check under sinks and around the water heater and toilets a few times a year, replace washing machine hoses that are cracked or bulging, and run each sprinkler zone each spring. A plumbing inspection is a good idea for older homes or before buying a house.

Secure Your Property to Avoid Further Water Damage

While you wait for the plumber, move furniture, rugs, valuables and electronics away from the water, contain drips with buckets and towels, and start drying the area with fans to slow mold growth. Stay out of standing water that is near outlets, extension cords or the electrical panel. Don’t touch the panel if you’re standing in water or the area is wet; call PG&E or an electrician to shut off power safely.

Leaks in San Jose Homes

• Slab foundations: many South Bay homes are built on slabs, and supply lines under the slab leak without visible water; warm floors and running-water sounds are the clues.
• Galvanized pipe: older South Bay homes’ corroded pipe leaks repeatedly.
• Irrigation: underground sprinkler leaks drive up summer water bills.

CPI Service finds and repairs leaks throughout San Jose and the South Bay. See leak detection, request a free estimate or call (408) 978-3093.