Telltale Signs of a Slab Leak and the Solution

Houses built on concrete slabs do not have basements. This makes it very difficult to know when there is a leak in one of the pipes that supply water to your fixtures and faucets?

Apart from that, detecting the exact location of the leak is not always easy and even when you do, you must engage the services of a professional which is not cheap. Fixing slab leaks is not something most homeowners can do on their own.

house floor
house floor

So, what are the signs of a slab leak and what can you do if you suspect you have a leaking water pipe in your slab?

If there is a spike in your water bill, your water pressure has reduced, there is a musty odor in the house, some spots on the floor are warmer than others or the floor is cracked, damp or warped, you most likely have a slab leak. The sound of trickling/running water when all faucets and appliances are turned off is another good sign.

Some slab leaks will go unnoticed for a long time especially if you don’t track your monthly water usage.

Slab leaks are usually caused by old corroded galvanized steel or copper pipes which are unable to contain the water pressure anymore. In areas that are prone to earthquakes, as the ground shifts, the water pipes are subjected to a lot of strain which causes them to shear or crack.

Related: How to find an underground water leak.

The best thing to do once you suspect that you have a slab leak is to contact a licensed plumber. A plumber will first locate the location of the leak and then advise you on the best way to fix it. Repairing a slab leak is quite expensive but the sooner you do it the better.

Fixing a slab leak costs between $650 and $4500. Detecting the location of the leak alone will cost between $150 and $600 while fixing it will cost anywhere between $500 and $400.The cost depends on the leak location and the amount of work involved to fix.

Slab leaks are usually not covered by homeowners insurance. They may however be covered if the home is damaged by a covered event which caused the leak. In instances where the leak is caused by neglected maintenance like old and corroded pipes then you are not covered.

Slab leaks can be quite dangerous especially when left unfixed for a long time. As the water seeps through the floor and walls, tiny cracks will start to develop and grow bigger in size with time resulting in extensive water damage.

How to Tell if You Have a Slab Leak


Slab leaks don’t have the same signs. Some are easier to detect than others. The following are the telltale signs that you have a leak in your slab:

1. Spinning Leak Detector

The easiest way to check if there is a leak in your house is by checking the water meter leak detector. A leak detector does not however help you locate the actual leak location but there is a something you can do to rule out other places.

To check if you have a leak in your house in the first place, locate your water meter and check if the leak detector is spinning. Before that, you will need to turn off all faucets in your property including washing machines, dishwashers and refrigerator icemaker.

A water meter is usually located between your house and the street, near the curb or sidewalk. It is found inside a concrete box with a metal or plastic lid with “Water” or “Water Meter” inscribed at the top. You could also have the water meter inside the garage.

  • Remove the water meter lid carefully as it is not unusual to find snakes or spiders underneath them.
  • Look for a small triangle (in some meters it looks like a gear) on the water meter. If it spinning, it means there is a leak somewhere. On the other hand if the leak detector is still, you have no leak.
water meter
  • If your water meter does not have a leak detector, check the meter reading and compare after about 30 minutes. Do not draw water from the house during that time. You have a leak if there is a difference in meter reading after the 30 minutes. Check out this post if you don’t know how to read a meter.

If you found out that there is a leak after the above test, you will next want to check if the leak is inside the house (slab leak) or outside the house (usually between the city water supply line and the shut off valve).

Locate your main house water shut off valve and turn it off. This valve will be located where the main water line enters the house.

Repeat the test above on the water meter. If the leak detector is still spinning, the leak is outside your house in the pipe buried in your yard.

On the other hand, if the leak detector stops, you have a leak inside your house and very much likely under the concrete slab.

2. Increased Water Bill

Has your water consumption increased the last few days but there is no increased water demand in your house (like guests or watering plants)? You most likely have a slab leak.

Since most people don’t track their daily water consumption, you will notice that your water bill has increased without an explanation if you have a slab leak.

The thing about water leaks is that no matter how slow the leak is, water is being lost every passing second. Over a period of one month the total volume of water lost will be quite substantial.

3. Reduced Water Pressure

Think about it. You will have more water pressure when only one faucet in the house is turned on that when you have several of them running. It is the same thing with a leak.

A leak in your slab will create an unwanted water demand under your floor, meaning less water will reach your faucets and appliances. If the leak is slow there may not be a significant reduction in water pressure.

One thing to know is that it is highly unlikely that there will be a reduction in pressure in both cold and hot water lines. Since only one pipe will be leaking, the low water pressure will only affect either the cold or hot water.

Low water pressure in the house does not always indicate that there is a leak. The problem could be caused by other factors as indicated in this post.

4. Warm Spots on the Floor

Hot water accelerates corrosion in pipes more than cold water. It is therefore true to say that most of the slab leaks will be caused by hot water lines more than cold water lines.

When a hot water pipe starts to leak, the hot water will heat up the concrete above it which is why you will have a warm spot on your floor. These types of leaks are usually the easiest to detect.

If you notice a hot/warm spot on your floor then you most likely have a leak in your slab. Depending on the flooring material you have, some leaks are easier to notice that others.

Hardwood and linoleum floors are the easiest not detect while carpeted or tiled floor are a little harder unless you have a serious leak.

You may also experience increased warmth or/and humidity in a certain room if there is a leaking hot water pipe underneath its floor.

A leak in your hot water pipe means that the water heater will be on for a long time. This is another sign of slab leak coupled with high energy bills.

5. Running/Trickling Water Sound

If you wake up in the middle of the night when it is all quiet outside and all faucets in your house are turned off but you can hear the sound of running water, you indeed have a leak. It is even more conclusive when you can trace it to the house’s slab.

While not all leaks can be heard, severe water leaks can be easily heard from inside the house. Such leaks should be repaired as soon as reasonably possible.

6. Pooling Water

When you have a leak in your slab, the water has to go somewhere. This water accumulates under the slab until it can’t hold any longer. You may therefore have a pool of water inside your house or outside.

If you have pooling water outside your house whose source you can tell or if seems to be seeping out of the house’s foundation, it is a good sign that you have a leak in your slab. Pooling water inside the house could be caused by leaking fixtures like toilets or fridges as well.

7. Musty Odor

A wet surface is the perfect condition for molds to thrive. A leak in your slab will saturate the floor with water and a result mold and mildew will start to grow under the carpets or floorboards.

If the leak is not fixed fast, the water will soak up the walls as well and an uncontrolled mold growth will be certain. It is not unusual for mold to grow in bathrooms but if you notice a musty smell in your house then a leak in the slab could be the cause.

8. Cracking Floors

As the water seeps through the concrete/foundation, it unsettles it causing it to shift and therefore cracks form. While cracks will always be there on floors as the foundation settles, sudden cracks are almost always caused by water leaks.

There could also be another phenomenon known as foundation heaving. This refers to a condition where the slab experiences a high degree of swelling occasioned by a severe slab leak and hence the building is slightly lifted.

A shifting building can cause cracks on the inside and on the outside. If you experience such signs it is important to contact the services of licensed professional immediately to advise you on the best way forward.

What to Do if You Have a Slab Leak

Once you suspect that you have a slab leak, my advice is to contact a plumber to help you locate and fix the problem. While fixing slab leaks is expensive, there is no other way to deal with the problem.

You can try to locate the exact location of the leak as that will save you some money but if you can’t just let the plumber do it. They have the experience and the tools to do it.

Usually, the plumber will turn off water to the house and drain the lines. They will then pump air inside the pipes and use special electronic and acoustic equipment to check where the air will be leaking from, which will be where the water was leaking from.

This prevents the tearing down of the entire floor in a bid to find the leak and that is why I don’t recommend you doing it on your own.

Please note that your house will be without water for the duration the pipes will be under repair. A good plumber may however use a plastic pipe to divert water from the pipes and into your house as the repair is ongoing.

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