A hidden leak shows its signs long before it shows water. Here are the telltale signs of a water leak inside and outside your West LA home, the free meter test that confirms one, and what to do next.
Written bySteven Lockhart·Reviewed byMiguel Lopez, Owner & Licensed Plumber (CSLB #974600)·Last reviewedJune 2026 · 6 min read
Quick Answer
The clearest signs of a water leak are a water bill that climbs with no change in habits, the sound of running water when everything is off, a meter that keeps moving after you shut all the water, a musty smell or mold, a warm spot on the floor, a drop in water pressure, or an unexplained greener patch of lawn. The fastest way to confirm one is the meter test — and any single sign is reason enough to check.
A concealed leak rarely announces itself with a puddle. On the Westside’s older homes it shows up indirectly — on the water bill, in the air, underfoot, or out in the yard — long before you ever see water. Knowing the signs of a water leak lets you catch it while the fix is still small. This guide is part of our complete resource on water leak detection in West Los Angeles.
A water leak is the continuous escape of water from a pressurized supply line, fixture, or fitting — often hidden in a wall, under a slab, or underground — that reveals itself through indirect signs before it becomes visible damage.
Indoors, the hidden leak warning signs cluster around water, sound, and smell. Watch for the sound of running water with every fixture off, a musty or mildew odor, bubbling paint or stained drywall, a sudden drop in pressure, or a warm patch on a tile or concrete floor — a classic hot-water slab leak. Any one of these is worth confirming with the meter test below.
Outdoors, leaks surface as a patch of lawn that is greener or soggier than the rest, water pooling with no rain, a constantly damp spot near the meter, or cracks appearing in a driveway or foundation. A buried supply or irrigation line can waste water for weeks while the only clue is a summer bill that will not come down.
| Sign | What it usually means | How urgent |
|---|---|---|
| Meter moves with all water off | An active hidden leak somewhere | Investigate promptly |
| Warm spot on the floor | Hot-water line leaking under the slab | Urgent — risks the foundation |
| Musty smell or mold | A leak that has run a while concealed | Address soon |
| Spiking water bill | Continuous loss you cannot see | Investigate now |
| Low water pressure | Supply-line leak or corrosion | Have it checked |
| Greener / soggy lawn patch | Buried irrigation or main-line leak | Locate soon |
A quick walk-through plus the meter test confirms most leaks in about an hour.
Note the meter reading, leave all water off for an hour, then read it again — movement means a leak.
Look under sinks, around toilets and the water heater, and at ceilings for damp, stains, or drips.
Listen for running water with everything off, and check for a musty smell, mold, or bubbling paint.
Look for soggy or unusually green patches and any damp ground near the meter or irrigation lines.
Not sure what you are looking at? We will pinpoint it before opening a wall.
Get a Free QuoteA Westwood homeowner notices a faint musty smell and a water bill that has crept up for two months, but sees no visible leak.
Walked through the meter test over the phone with New Pro, the homeowner confirms the meter is still moving with all water off, and we acoustically pinpoint a concealed leak inside a bathroom wall.
The leak is repaired through one small opening before it reached the framing, and the bill and the smell are gone by the next cycle.
The Bottom Line
The signs of a water leak are easy to miss one at a time but hard to ignore together — a creeping bill, a musty smell, a warm floor, a meter that will not sit still. Run the meter test the moment you suspect one, and if it confirms a leak, New Pro will pinpoint the source precisely and quote a flat rate before any work begins. Call any time.
An unexplained jump in your water bill, the sound of running water with everything off, a meter that keeps moving after you shut all the water, a musty smell or mold, a warm spot on the floor, low water pressure, and unusually green or soggy patches of lawn. Any single one is worth confirming.
Run the meter test: note your meter reading, leave all water off for about an hour, then read it again. If the numbers moved or the small leak dial spun, water is escaping somewhere concealed and should be located before it causes damage.
Often, yes. A warm patch on a tile or concrete floor usually means a hot-water line is leaking beneath the slab. Because the water is trapped under the foundation, this type of leak is worth locating quickly to avoid structural damage.
Yes. A leak hidden in a wall, ceiling, or under a floor keeps materials damp, which leads to mildew and mold and the musty odor that comes with them. A persistent musty smell with no obvious source is a common sign of a concealed leak.
It can. A drop in pressure throughout the house may point to a leak or corrosion in a supply line, especially in older galvanized plumbing common on the Westside. If pressure falls off with no other explanation, it is worth having the line checked.
Run the meter test to confirm water is escaping, then call for professional leak detection. We pinpoint the source precisely so the repair stays small, and we confirm a flat-rate price in writing before any work begins.
Written by the New Pro Plumbing content team and reviewed for technical accuracy by Miguel Lopez, owner and California-licensed plumber (CSLB #974600). Statistics are cited to the U.S. EPA and figures reflect typical West LA conditions, not a quote — we confirm pricing in writing before any work begins.
What's new: June 2026 — first publication.
If the meter's moving with everything off, water is escaping. New Pro pinpoints the source and quotes a flat rate before we start — call any time, day or night.
