A high water bill can be one of the first signs of a hidden water leak. If your household habits have not changed but your water usage has increased, water may be escaping from a pipe, toilet, appliance connection, irrigation line, hot water system or concealed area under floors or behind walls.
According to the team at 100% Plumbing, hidden leaks are often more expensive when they are ignored. Early signs such as damp patches, low water pressure, running water sounds, musty smells or a moving water meter can help homeowners act before the leak causes property damage. If you suspect a hidden leak, our professional plumbing services in Calpe and the Costa Blanca can inspect the system and recommend the safest next step.
100% Plumbing S.L. is based in Calpe, Alicante, and provides plumbing, repairs, installations and maintenance services across the Costa Blanca, with a 24-hour emergency helpline available for urgent issues.
Can a Hidden Leak Cause a High Water Bill?
Yes. A hidden water leak can cause a high water bill because water may be escaping continuously even when taps and appliances are not being used. Common sources include running toilets, leaking pipe joints, slab leaks, underground supply leaks, faulty water heaters, irrigation leaks and appliance hose leaks.
The U.S. Environmental Protection Agency’s WaterSense programme states that household leaks can waste nearly 1 trillion gallons of water annually across the United States, and that the average household’s leaks can waste nearly 10,000 gallons of water every year. WaterSense also recommends checking the water meter before and after a two-hour period when no water is being used to help identify leaks.
If your bill has increased suddenly, do not wait for visible water damage. A leak may already be active.
Why Hidden Leaks Are Easy to Miss
Not every leak creates a puddle. Many hidden leaks happen behind walls, under floors, below concrete slabs, inside cupboards, near water heaters or in outdoor supply lines. These leaks can run for weeks before they are noticed.
Hidden leaks are common because:
- Pipes may be concealed behind walls or under floors
- Small leaks can evaporate before forming puddles
- Toilets can leak silently into the bowl
- Outdoor irrigation leaks may soak into soil
- Water heater leaks may start slowly
- Holiday homes may sit empty for long periods
- Hard water and limescale can affect valves, joints and appliances
For properties in Calpe and across the Costa Blanca, long vacancy periods and hard water can make early leak checks especially important. Our guide to plumbing maintenance for holiday homes in Calpe and Costa Blanca explains how owners can reduce risk before leaving a property empty.
Warning Signs of a Hidden Water Leak
A hidden leak may show several small warning signs before it becomes obvious.
| Warning sign | What it may mean | Best next step |
|---|---|---|
| Higher water bill | Water is being used or lost unexpectedly | Compare usage and test the meter |
| Meter moves when water is off | Leak somewhere in the system | Isolate water use and call a plumber |
| Damp walls or floors | Hidden pipe, slab or appliance leak | Inspect area and avoid delay |
| Musty smell | Moisture trapped behind surfaces | Check for damp and mould |
| Low water pressure | Water escaping before reaching fixtures | Check if one or all fixtures are affected |
| Running water sounds | Concealed pipe leak or toilet leak | Turn off fixtures and listen |
| Warm floor patch | Possible hot water line under slab | Arrange leak detection |
| Mould or staining | Long-term moisture | Locate source, not just surface clean |
| Toilet keeps refilling | Internal toilet leak | Check cistern mechanism |
| Water heater area damp | Tank, valve or connection leak | Inspect and call if active |
This table helps separate normal household changes from signs that need plumbing attention.
1. Your Water Bill Has Increased Without a Clear Reason
A sudden or steady increase in your water bill is one of the strongest early indicators of a hidden leak. Bills may rise because of seasonal use, guests, irrigation or pool filling, but if none of those apply, a leak should be considered.
What to check:
Compare your current bill with the same period last year, not just the previous month. Holiday homes and rental properties can have seasonal water-use patterns, so context matters.
Best next step:
If usage is higher and you cannot explain it, perform a water meter test and inspect toilets, taps, appliance connections and outdoor water points.
For wider water supply concerns, our domestic water supply plumbing service can help identify whether the issue is inside the home, near the supply line or connected to a fixture.
2. The Water Meter Moves When Everything Is Off
A water meter test is one of the simplest ways to check whether water may be escaping.
How to do a basic water meter leak test:
- Turn off all taps, showers and appliances.
- Make sure toilets are not refilling.
- Do not use washing machines, dishwashers or irrigation.
- Check the water meter reading.
- Wait at least two hours without using water.
- Check the meter again.
If the meter changes while no water is being used, there may be a leak.
The EPA WaterSense programme recommends checking the water meter before and after a two-hour period with no water use as part of its household leak checks.
If the meter moves but you cannot see a leak, the problem may be concealed under floors, behind walls, outdoors or inside a toilet cistern.
3. You Hear Water Running When No Taps Are Open
The sound of running, dripping, hissing or rushing water can indicate a concealed leak. This is especially important if the sound continues when all fixtures are off.
What to check:
Listen near bathrooms, kitchens, utility areas, water heaters, exterior walls and meter boxes. Also listen after flushing toilets to see whether the cistern stops filling.
Best next step:
If the sound continues, avoid opening walls or floors yourself. A plumber can use professional methods to narrow down the source with less disruption.
If the sound seems to come from a toilet, our guide toilet keeps running? simple checks before calling a plumber explains what to check safely.
4. Damp Patches, Stains or Musty Smells Appear
Hidden leaks often show as moisture before visible dripping appears. Damp walls, warped flooring, ceiling stains, peeling paint, swollen skirting boards and musty smells can all point to a concealed leak.
What to check:
Look around bathrooms, kitchens, utility rooms, water heaters, wardrobes, ceilings below bathrooms and walls near pipe routes.
Best next step:
Do not only repaint or dry the area. The source needs to be found. If dampness appears without an obvious cause, arrange leak detection before the damage spreads.
For concealed leaks under floors or concrete, read our guide on how to detect a slab leak before it damages your property.
5. Water Pressure Has Dropped
Low water pressure can happen for several reasons, but a hidden leak is one possible cause. If water is escaping before it reaches taps or showers, pressure may fall across the property.
What to check:
Notice whether low pressure affects one tap, one bathroom, hot water only, cold water only or the whole home.
Best next step:
If the pressure drop affects several fixtures or appears suddenly, call a plumber. The issue may be a leak, valve problem, limescale restriction or supply fault.
Hard water can also reduce flow over time by contributing to limescale inside pipes and fixtures. For local context, see how hard water affects pipes, boilers and appliances in Costa Blanca homes.
6. A Toilet Keeps Refilling or Running
A running toilet is one of the most common causes of water waste. It may not look like a leak because water often runs silently from the cistern into the bowl.
The EPA WaterSense home maintenance guidance advises investigating toilets that constantly run, do not flush properly, or show water continuously flowing into the overflow tube.
What to check:
Listen for refilling sounds after the toilet has already flushed. You can also place a few drops of food colouring in the cistern and wait without flushing. If colour appears in the bowl, water is leaking through.
Best next step:
A faulty flapper, fill valve or flush mechanism may need adjustment or replacement.
7. The Water Heater or Boiler Area Is Damp
Leaks near water heaters or boilers can start small. A valve, pipe connection, pressure relief valve or tank may drip slowly before a larger failure happens.
What to check:
Look for damp flooring, rust, staining, dripping valves, pressure changes, unusual noises or inconsistent hot water.
Best next step:
Do not ignore water around a hot water system, especially near electrical components or gas appliances. For diagnosis, visit our hot water systems services in Calpe and the Costa Blanca.
If your system is older or unreliable, our guide to signs your water heater needs repair or replacement can help you decide what to do next.
8. Outdoor Areas Are Wet When They Should Be Dry
Outdoor leaks can be harder to notice because water may soak into soil, garden areas, terraces or irrigation zones.
What to check:
Look for unusually green patches of grass, wet soil, puddles near exterior walls, dripping outdoor taps, irrigation that runs unexpectedly or water near the meter box.
Best next step:
If the meter moves while all indoor and outdoor water use is off, an underground supply line or irrigation leak may be possible.
Holiday homes with garden watering systems should be checked carefully before and after long vacancy periods.
What to Check Before Calling a Plumber
Before calling a plumber, gather simple information that can speed up diagnosis.
Check:
- When the bill increased
- Whether the meter moves when water is off
- Whether damp patches are growing
- Whether pressure changed suddenly
- Whether the issue affects hot or cold water
- Whether any toilet keeps running
- Whether irrigation or outdoor taps may be involved
- Whether the water heater area is dry
- Whether the property was empty for a long period
Do not break tiles, open walls or dig outside without diagnosis. This can cause extra damage and may not find the leak.
If a leak is active or water is spreading, locate and use the main shut-off valve. Our guide what is a stopcock and why every homeowner should know where it is explains how the stopcock helps isolate water in an emergency.
When Is a Hidden Water Leak an Emergency?
A hidden leak should be treated as urgent if there is visible water damage, water near electrics, a ceiling stain that is growing, a major pressure drop, water pooling around a boiler or water heater, or the meter continues moving when the home is not using water.
You should also act quickly if the property is a holiday home or rental and may be left empty again soon.
If you are unsure whether the situation is urgent, read our guide on when to call a professional plumber.
For active leaks, turn off the water supply if safe and contact the team through the 100% Plumbing contact page.
Hidden Leak Detection in Calpe and the Costa Blanca
100% Plumbing helps homeowners, landlords, property managers and holiday-home owners in Calpe and across the Costa Blanca investigate hidden leaks, unexplained high water bills, low water pressure, damp patches, slab leaks, running toilets and hot water system leaks.
Our team can inspect visible pipework, test common leak points, assess water pressure, check shut-off valves and recommend practical next steps. If the issue is linked to ageing pipework, we can also advise whether a targeted repair or pipe replacement is the better long-term option.
For older systems, our guide on whether to repair or replace old plumbing pipes explains the warning signs that repairs may no longer be enough.
FAQ About Hidden Water Leaks and High Bills
Can a hidden leak cause a high water bill?
Yes. A hidden leak can cause a high water bill because water may escape continuously from pipes, toilets, appliances, irrigation lines, water heaters or concealed areas behind walls and floors.
How can I tell if I have a hidden water leak?
Warning signs include a higher water bill, a moving water meter when water is off, damp patches, musty smells, low water pressure, running water sounds, warm floor areas or toilets that keep refilling.
How do I check my water meter for a leak?
Turn off all taps, toilets, appliances and irrigation. Check the water meter, wait at least two hours without using water, then check it again. If the reading changes, there may be a leak.
Can a running toilet increase my water bill?
Yes. A running toilet can waste water continuously, often without visible puddles. If the cistern keeps refilling or water flows into the bowl after flushing, it should be repaired.
Is low water pressure a sign of a hidden leak?
Low water pressure can be a sign of a hidden leak, especially if it affects several fixtures or appears suddenly. It can also be caused by limescale, valves or supply problems.
Should I turn off the water if I suspect a hidden leak?
If there is active leaking, spreading dampness, water near electrics or a fast-moving meter, turn off the main water supply if safe and call a plumber.
Who should I call for hidden leak detection?
You should call a qualified plumber with experience in leak diagnosis. A professional can check the water system, locate likely leak sources and recommend the safest repair.
Final Advice from 100% Plumbing
A high water bill is often the first clue that something is wrong. If your water use has not changed, check the meter, listen for running water, inspect toilets, look for damp patches and review outdoor taps or irrigation.
Hidden leaks are easier and usually cheaper to deal with when found early. For hidden water leaks, unexplained high bills, slab leaks, running toilets or plumbing inspections in Calpe and across the Costa Blanca, contact 100% Plumbing.
Need help finding a hidden leak? Contact 100% Plumbing for reliable professional plumbing services in Calpe and the Costa Blanca.
