.png)
Hidden Water Leak Signs: High Bill, Wet Spots, Mold Smell, and Slab Leak Clues
- Oliver Owens
- Jul 30
- 9 min read
A hidden water leak rarely announces itself
Some leaks are obvious. Pipes burst, water shoots out, and the situation is rarely
mysterious. Hidden leaks, however, begin their slow work, often far from view. They can
originate behind a wall, under a slab, beneath a vanity, inside an irrigation line, or anywhere
within the home’s water supply system. By the time the signs show, water has already been
wasted, the bill has grown, and the drywall and floors soaked.
Kramer’s Plumbing hears similar complaints from homeowners and business owners
throughout Placentia, CA and North Orange County:
“My water bill jumped, but we didn’t use more water.”
“There is a strange dampness in our home.”
“The floor in this room is always warm.”
“There is a strange musty smell, but we don’t see any water.”
These are all signs that it is time to investigate.
This blog serves as a guide to the warning signs of a serious hidden water leak. It is also helpful if you want to know what to do next and when to call a plumber. In most cases, it’s best to stop leaks before they become expensive jobs.
The first big sign is a jump in your water bill
High water bills are one of the most obvious signs of a hidden water leak.
The challenge with this type of leak is that it can be hard to see, although it can waste
considerable water. For example, according to the EPA, the average household has leaks
that waste more than 10,000 gallons of water every year. And 10% of these homes have
leaks that waste more than 90 gallons of water daily.
So, a leak is not always a torrent. Instead, it can be as simple as a small drip that soaks the
floor and contributes to a growing bill.
What to check
As with most issues, the first step is a visual inspection, asking yourself the following questions:
Did we add people to our household?
Was there a significant increase in lawn or landscape watering?
Did you fill a pool during the time period?
Is there otherwise an obvious explanation for an increased water usage?
If not, it is time to look closer.
A high water bill does not always mean your home has a leak, but it is one of those situations where it is time to start investigating.
The second sign is a water meter that’s
mysteriously running
This is one of the most helpful signs for any homeowner to check.
Turn off all water sources, both inside and outside the home or business. Once you have
done this, check the water meter. Is it running?
A running meter means water is continuing to flow somewhere, which should prompt an
investigation.
If your water meter has a small indicator for leaks, it can help you know the severity of the
leak.
One caution
If you are not confident about checking the meter yourself or the meter box is inaccessible
or obstructed, contact a plumber or water company to help.
The third sign is visible evidence, such as wet
spots, soft floors, or bubbling paint
Visible evidence is always a good sign when it comes to leaks.
Wet spots on drywall, bubbling paint, soft spots on the floor, swollen baseboards, ceiling
stains or watermarks from an upstairs bathroom, wet areas inside a cabinet, or strangely
moist ground in the landscape are all potential signs of a hidden water leak.
The critical point is that these marks continue to appear, which means water is regularly
invading these areas.
A spill will dry, but a leak will leave dampness that reappears.
The fourth sign is a musty smell or a moldy odor
Often, a strange smell is the first sign of a hidden water leak.
Musty smells indicate dampness. Leaks and damp weather ruin drywall and furniture.
According to the EPA, the key to preventing mold is to remove wet or damp objects within 24
to 48 hours of the initial leak or spill. Similarly, the EPA highlights the importance of fixing
plumbing leaks to control mold.
Where to find them
Musty smells can be found in a variety of areas:
Behind vanities
Inside cabinets
Near water heaters
In closets that touch water heater locations
Along baseboards
Near showers and tubs
A musty smell is not always a sign of a leak, but it can be one. Venting, roof leaks, condensation, and old water damage can also be potential sources. The location can be an indicator.
The fifth sign links low water pressure with strangely timed occurrences
Low water pressure can be a sign of a leak, but there are a variety of other causes. Still, if
you begin to experience strange drops in water pressure, it is a good idea to check for
hidden water leaks.
A leak in the home’s plumbing system always reduces the pressure somewhere. And while
this issue may begin in one area, it often grows and encompasses the entire house.
Other signs to watch for
Sudden loss of water pressure
Loss of pressure that appears in only one area of the home
Changes in water pressure from hour to hour
Hot water pressure being noticeably different from cold water pressure
A combination of low pressure with strange wetness or a high water bill also indicates a problem
The sixth sign is a warm spot on the floor
Warmer spots on the floor can be an indicator that a hot water line is leaking underneath.
Slab leaks represent one type of hidden water leak. In slab leaks, the supply line beneath the
slab is compromised and requires a trip underneath the home or business to begin repairs.
In Southern California, supply lines run under the slab, so a hidden water leak can lead to
sudden increases in the water bill and warm spots on the floor. A warm spot can be an
indicator of a hot water line leak.
In addition to warm spots, other signs of slab leaks are:
Hearing running water when no fixtures are running
High water bills
Floor damage
Wet carpet
Musty smell
Cracks or changes to the floor
Hot water heater running frequently
A warm spot on the floor combined with a high water bill is a good reason to call a plumber.
The seventh sign is that the water heater seems to be running more frequently
The water heater can provide a few hints to hidden hot water leaks. If there is a leak in the
hot water supply line, the water heater has to produce more hot water to compensate for the
loss.
This is especially true if the hot water line leaks before reaching the various hot water
faucets.
If your water heater appears to be running more than normal and you are also having an increase in water costs, it is time to investigate the hot water supply line.
The eighth sign is a perpetually running toilet
Toilets can also be silent sources of water waste. If the toilet is running perpetually or
seems to be running when it should not, it could be a sign of a hidden water leak.
Even the most frequent toilet user should not have continuous water loss.
A few signs of a running toilet are:
The need to constantly re-fill the toilet
A running sound when the toilet should be silent
Water ripples in the toilet bowl
A random refill during the night
A sudden rise in your water bill with little or no reason
A test is simple: add food coloring to the toilet tank. Wait for a while without flushing. If the water in the bowl changes color, there is a leak allowing water to escape from the tank into the bowl.
What to do if you suspect a water leak
Here are a few basic first steps:
Turn off all the water and check the meter
If the meter continues to run when all water is turned off, you have water loss somewhere.
Check all the toilets
Toilets are frequent sources of water loss.
Look under all the sinks and at the appliances
Check the vanity, the cabinets, the water heater, the refrigerator line, the dishwasher, and the laundry connections.
Walk the perimeter and check for damp soil, unusually green areas, or irrigation that is still wet
Pay attention to strange smells
Musty or earthy smells are often associated with water damage. The location will help determine the type of leak.
Call a plumber if you can’t pinpoint the issue
If the bill is rising for no apparent reason and the water meter is also suggesting water loss, contact a professional plumber.
What NOT to do
Do not ignore a high water bill
Even if the water bill is unexpectedly high, you should investigate the cause.
Do not paint over water spots
If you paint over the water spot to hide it, the leak will still occur, soaking the new paint.
Do not assume strange mold smells are “just the house”
A strange, musty smell often means there is excessive moisture nearby. Water damage will always lead to mold.
Do not open walls and cabinets at random
A professional plumber can identify the likely source of the leak, which can reduce the damage and unnecessary opening.
Do not ignore water near electrical outlets, circuits, or panels
Water and electricity are dangerous when mixed, so contact a qualified electrician and plumber. The situation is even more urgent if you see water near the main circuit breaker or power panel.
When to call Kramer’s Plumbing
Kramer’s Plumbing should be called if you have:
A sudden jump in the water bill
A water meter showing water loss when all fixtures are turned off
Visible damp spots, watermarks, bubbling paint, or other signs of water damage
Musty smells, especially near plumbing fixtures
Hearing running water when no fixtures are running
Noticing warm spots on the floor
Sudden drops in water pressure or a noticeable difference between hot and cold water pressure
A water heater that appears to be running more frequently than normal
When we arrive, we begin by analyzing the pattern of the leak and look at the most likely
sources of water loss. If necessary, we isolate the problem area and investigate plumbing
fixtures, lines, and other potential sources of water damage. Our goal is to help detect leaks
at the fixture, water heater, or line level and reduce the damage. We do not believe in
unnecessary destruction, so we do everything possible to locate the leak and advise on its
repair.
FAQ: Hidden water leak signs
Why did my water bill suddenly increase?
The sudden jump could be associated with irrigation, extra people in the home, meter or reading error, or a hidden water leak. A thorough inspection of the meter and toilets is always the first step in identifying the cause.
How can I tell if I have a hidden leak?
The most reliable test is to turn off all the water and see if the meter continues to run. If this is the case, the plumbing is losing water somewhere, which is often the result of a hidden leak.
Can a small leak really cause mold?
Unfortunately, yes. Mold feeds on moisture, and the EPA reminds us that the most basic way to prevent mold is to stop plumbing leaks and dry wet areas of the house within 24-48 hours of the initial leak or spill. According to the EPA, the best way to deal with mold is to address the source of the problem and then clean and dry all affected objects.
What does a slab leak feel like?
A slab leak may be accompanied by warm spots on the floor or dampness, water loss without an obvious reason, unusual sounds, and the water heater running continuously.
Does low water pressure mean I have a leak?
Low water pressure can have several causes, including regulator issues, closed valves, and clogged fixtures. However, if the water pressure is suddenly low somewhere in the house, especially if combined with a high water bill, it can be a sign of a hidden leak.
Can a toilet leak quietly?
Yes. A toilet can leak continuously without making much noise, wasting considerable water in the process. A simple test is to add a few drops of food coloring to the toilet tank.
Should I call a plumber to find the leak before I attempt to repair it?
Yes. It is always a good idea to locate the source of the leak before attempting to repair it, as a qualified plumber can often help reduce the damage during the repair.
Is a hidden leak in the house an emergency situation?
It can be if the water is spreading, soaking the house, exposing electrical outlets or panels, or damaging hardwood flooring.
Call Kramer’s Plumbing for hidden leak detection in Placentia, CA
When the water bill rises unexpectedly, strange dampness appears, or a musty smell fills the
air with no apparent explanation, call Kramer’s Plumbing. We can help locate the source and
recommend the most effective repair to keep your water bill from rising.
Kramer’s Plumbing is locally owned and family-run, serving the residents of Placentia and
the surrounding North Orange County area, including Fullerton, Brea, Yorba Linda, Anaheim
Hills, and more.
Call (714) 260-3986 or visit the contact page to request an inspection or service.
Free supporting backlinks for this post
Include the following backlinks to external websites:
EPA mold and moisture guide: explains why leaks and damp materials should be dried quickly to help prevent mold growth.
EPA mold cleanup steps: recommends fixing plumbing leaks and other water problems as soon as possible.
EPA household leak estimate: notes that average household leaks can waste more than 10,000 gallons per year.
Kramer’s Plumbing About page: supports local trust signals, including over two decades serving Placentia and surrounding areas.
Comments