Your fresh water system runs on a pressurized system. It pumps clean water from the city/meter into your home. The pipes are always full of water and ready to flow once you turn on the faucet to wash your hands, clean the dishes, and take a bath or shower. It also flushes your toilet and is ready when you start the washing machine to do laundry.

If there is a leak above your home’s concrete slab from your fresh water pipes, you will most certainly have water on a floor or somewhere else. And because there is always water in this pressurized system, the water never stops flowing or dries up. Having a leak in a fresh water pipe is like turning on the faucet and leaving it on.

Now it is possible that the puddle is the result of a fresh water leak under the concrete slab. However, this is rarely the case. It’s far more likely the puddle is a result of a leak above the slab.

With a leak under the slab, the water from the leak would have to build up enough to the point that it needs to find a path out. An under slab leak resulting in a puddle on your floor would mean that the only path out was up. Add to that the water then had to make it through 4 or 5 inches of thick concrete slab.

Again, while it is possible and has happened from time to time, keep in mind water typically flows downhill and not up. So it’s unlikely the only path out is up. Also there would already have to be some some sort of crack running all the way through the slab.

So what you want to look for here is if the puddle is the result of water that is continually flowing. If a particular area is flowing non-stop for a minimum of a few days—and it is not raining outside—it is very likely you have a fresh water leak.

The question then becomes is the leak above or below the concrete slab. For this, you most likely need a professional to come out to determine this.

However—while this isn’t a guaranteed method to determine this on your own—if you turn off the water, and the water stops flowing or dries up, that is another sign that you have a fresh water leak.

And if once you turn the water back on, water floods the floor in less than one minute, that’s a good indicator that the leak is above the slab.

Above Slab Sewer Line Leak

We often get calls from clients asking us to check their under slab sewer system for leaks because they have water on or above the slab.

As mentioned above, a fresh water pipe always has water in it. A sewer line on the other hand does not have water in it unless you are running water somewhere in the house like a faucet, washer, or toilets, etc.

Your sewer pipes work with the power of gravity so that the waste and water flow downhill out of your system to the city line and ultimately to the waste treatment plant.

Because—as mentioned above—water flows downhill and not up, and this piping system is not pressurized or full of water, any water that leaks out of this type of system under a slab in mass quantities ultimately leaks back into the sewer system like a rain water drainage system and flushes out.

The only possible way a sewer leak under the slab can cause water to flood above the slab is if the sewer line not only has a leak, but is also blocked so it can’t flow properly. In this case, every time the system is used, water flows to the stoppage.

And with nowhere to go, it forces its way out of the leak and into the soil. But it won’t be able to leach back into the sewer line because the line’s already full from of the blockage.

Then at some point, although most likely not right away, the water under the slab would build up so much that the area cannot accommodate it anymore. It would then have to find a place to go as more water flows into the system. And that place could be through a crack in the slab.

If this is the case, you will only find water on the slab when you use whatever is leaking. Unlike a fresh water leak where the water keeps pooling and never dries up, an above slab sewer leak won’t be constant and might dry up completely.

However, all that said, it is highly unlikely that a blockage in a sewer line would go undetected long enough for it to cause this kind of situation. So, although it is possible, it is very unlikely that a sewer leak below the slab will cause water to get above the slab.

In most cases, if you have water pooling from an under slab sewer system leak, the water will be very close to a plumbing fixture of some kind, like a sink, shower, toilet, tub, or a washing machine.

If it is close to your washer, it could be that the problem is the appliance itself and not the plumbing. Try pulling the machine out from the wall and remove the drain hose which runs from the washer to the pipe in the wall.

Then pour water in or put in a water hose and run water down the drain to see if water leaks out from anywhere. If it doesn’t, reconnect the washer and run it as normal. And if the leak occurs again, the problem is probably with your washing machine and not plumbing.

If your mysterious water is close to one or more of the other fixtures—and not flowing constantly—try not using one of the fixtures for a few days, and see if by not using it the water dries up. If it does, then the problem is sewer drain related with that fixture.

Just make sure you do this one fixture at a time, or you won’t know which is causing the problem.

Tubs and Showers

A standalone shower made of tile has a vinyl shower pan liner under the tile on the floor and about 12 inches up the wall. This is commonly called a tile shower pan.

It is very common for these shower pans to leak. When this happens, it’s a lot like a sewer leak in that it only leaks when the shower is in use. If your shower pan starts leaking, you’ll find water on the floor on either or all sides of the shower. This also includes other rooms that touch one side or another of the shower.

There is one easy way for you to determine if you have a shower pan leak. First, dry all the tile at and around the drain of the shower very well.

Then get some really good duct tape, and securely tape over the shower drain and the surrounding tiles.

After sealing the drain, turn on the water and fill the shower pan up with water. Just be sure you don’t fill it over the step-in curb level so water doesn’t overflow out of the shower.

Once filled, mark the water level and watch it to see if it will drop. Also look around the shower on all sides while you are waiting. Check for any water on the floor if the water level drops. If you see water dripping on the floor, then you probably have a shower pan leak.

However, make sure water is not leaking out around the duct tape. You want to make sure any drop in water level is from a leak and not the duct tape.

But if you filled the pan up to the highest point possible without it overflowing, and no water gets on the floor anywhere (especially if this is a slab foundation), then you probably don’t have a shower pan leak.

Now let’s talk about cracks in the grout or tile as well as tile issues of any kind. If there are tile issues of any kind, it is possible that when the shower is in use water is seeping into the wall and leaking out of the shower from there. This applies to a tub shower as well.

It is also possible that water won’t be visible on the slab initially when there are tile issues. But as time goes on, you’ll start to notice the water.

For tile issues, including missing caulk in the corners, get a good tile and shower expert out as soon as possible to prevent any water leaking issues and mold and mildew issues.

Another possibility to look out for as it relates to tubs and showers is water spilling or spraying on the floor during use.

This could happen for a number of reasons but is easily checked by two people; with one person in the shower and the other watching outside the shower.

You could also try running the shower positioning the head to spray up against the walls—including the door or curtain. Then stand outside the shower and watch for water.

Also check the other rooms next to the wall you are spraying. You want to make sure the water is not seeping into those rooms through the wall.

Air Conditioning Condensation

If you find puddles any time the air conditioning isn’t in use, this isn’t the cause of your mystery puddle.

When an air conditioner is in use, the A/C unit, via condensation creates water which it has to dispose off. Air conditioning units come with a primary drain pan to collect the water. And there is a drain outlet connected to a drain line where the water runs out of.

Normally the primary drain empties into a sewer system somewhere. This could be a bathtub drain or a washer drain if the unit is in the attic. But if it is in a closet, it usually drains right into the sewer system under the slab at the closet, or it will drain literally through the slab to the outside where the main sewer cleanouts are located.

If the unit is in the attic, there’s usually a secondary drain pan called a backup drain pan. It’s installed under the A/C unit with a drain running outside in case the primary drain line clogs up.

This insures the drain pan won’t overflow and flood your home when in use; although it is possible most air conditioning units in a closet do not have a secondary or backup drain pan.

Often these air conditioning drains get clogged. So if the air conditioning is running, it is creating water via condensation. And the water has to go somewhere which would likely be out of the unit onto the ceiling or floor.

So if you see a mysterious puddle near your A/C unit, it’s most likely a clogged air conditioning drain.

The problem here is knowing the right person to call to fix your air conditioning drain. Some parts of a condensation line can only be cleaned out by an HVAC Tech or A/C repair specialist, while some must be cleaned out out by a plumber.

Generally there are two types of pipes; a ¾ inch drain line and a 2 inch drain line. Most, if not all plumbers, don’t have the tools needed to clean out a ¾ inch drain line. Unless you know for sure the clog is in a 2 inch drain line, call an HVAC tech first.

However, if this happens during the heat of summer and the earliest appointment you can get is a week or two out, you can always try a plumber. It’s possible that plumber can solve the problem sooner. But if you do this, stay on schedule with the air conditioning technician. Don’t cancel until you know that the plumber can rectify the issue completely.

Rain Water

If the puddle or area of water only occurs when it rains, your mystery puddle probably isn’t a plumbing issue.

Here are some of the possible causes and things to look out for in these situations. Water is leaking into your home through the walls, chimney, roof, windows, etc.

Another common issue we see is water coming in through the brick ledge; that is the point where a brick wall and the slab meet. There should be 2 inches of concrete slab showing between where the slab and the bricks meet. The brick ledge should slope slightly away from the house.

First make sure the 2 inches of concrete slab—the brick ledge—is showing. Then see if the brick ledge and the soil around it slopes towards the house or if it is flat. If water pools in these areas when it rains, contact a rain water drainage expert. A rain water expert can evaluate your situation and determine what to do.

Also if the puddle is because of rain, you won’t see water pooling on a regular basis. Also why you should call a rain water drainage expert and not a plumber.

Sprinklers and Irrigation

It is not uncommon for sprinkler heads to spray water right onto the house. Check for this problem by running your sprinkler system and looking at each of the heads. Also check the inside of the house for water while the system is running.

It is possible the water might not be spraying onto the slab or wall at all. Instead it might be pooling in an area and causing water to flow into the house. So look out for pooling spots as well as any sprinkler heads spraying on the house.

Neighbor Leaks

Although this is extremely rare, it is possible. There have been instances where a leak from a neighbor’s house causes mystery water puddles in your home or lawn. This could happen if you live at the bottom of a hill and a house above you has a leak. It’s possible that leak is draining down to your home.

Other things that could cause water to pool around your home are swimming pool leaks or underground springs or creeks. These could cause water to pool around/under a foundation ultimately getting water into a house and onto a slab.

Although these are possibilities, it is highly unlikely to cause any water puddles inside a home.

There certainly are other factors that cause water puddles not listed here. However, anything not in this post is so rare and can only be determined after first eliminating all of the above possibilities.

If you have any questions about water leaks, give us a call the professional plumbers at Discount Plumbers in the Minneapolis/Saint Paul area. We are happy to discuss any issues you’re having, and always keep your specific needs and budget in mind.