What Causes a Basement to Leak or Flood?

Do you have water in your basement or a musty odor?

Finding water leaking into your basement is an alarming problem in your home. Whether it is water droplets, a slow leak, or a flood, water in the basement can cause a whole host of problems including ruined carpet, drywall, framing, and dreaded mold.

The first step is to locate the source of the water and then figure out how to stop it.

In this article, we will identify the causes of wet basement problems and provide cheap and affordable solutions to fix basement flooding and prevent it from happening again.

What are the signs of the source of the basement water leak?

  • Efflorescence
  • Leaks in the plumbing system
  • Peeling paint
  • Mold & mildew
  • Water deposits
  • Water stains
  • Chunks of concrete falling off

How do you find the source of a basement water leak?

Here are the steps you can take to find the source of the water leak.

Check for efflorescence

What is efflorescence? Efflorescence is the result of minerals being carried to the surface by moisture. The effect is a white powder or rust-colored stain on bricks or concrete. This is an indication of excess moisture problems. If the area is wet around it, this may be where the water leak source is.

Keep a lookout for cracks as efflorescence is also a sign of danger to structural integrity. Three conditions must be present for it to occur:

  • water-soluble salts present somewhere in the wall
  • enough moisture in the wall to create a soluble salt solution
  • a path for it to travel to the surface, evaporate, then crystallize
How do you clean efflorescence?
There are two options in cleaning efflorescence: sandblasting or chemical cleaners.  Use caution when sandblasting as it increases the porous quality of the masonry and should be followed with a waterproofing material.

An effective conventional chemical cleaner is muriatic acid in a mild solution: one part muriatic acid (hydrochloric acid, HC1) to 12 parts water. It is crucial to presoak with water and thoroughly clean with water post chemical use.

Even though you take the steps to remove and clean the efflorescence evidence, the root of the problem remains: water is entering through the wall from the outside.

This could result from:

  • Cracks in the wall
  • Hydrostatic water pressure
  • Tree roots
  • Foundation issues (addressed separately in this article)
  • Space at mortar joints
  • Gaps in grout

Once you find the culprit and fix the problem, make sure to use a proper high-quality waterproofing sealer for the basement walls.

Check for leaks in your plumbing system

Inspect your plumbing system thoroughly starting with its entry into the basement to where it leaves including the sewer line. As you do this, check for any leaky joints. To check the main water line, go outside and see if there is any water pooling around your home.  

Plumbing leaks are usually obvious with backed-up drains, burst pipes, and leaky fixtures. These problems result in a large amount of water in a short amount of time. Perpetual dampness may result from improperly sealed pipe penetrations, a hot water heater, bursting washer hoses, a utility sink, or a bathroom.

How do you fix leaky plumbing?

You can either call a local professional plumber or with simple plumbing issues, you can try to do it yourself.

Here are four simple DIY plumbing fixes:

Remember to turn water lines off while completing your plumbing projects.

1. Use a slip coupling on pipe

  • A slip coupling is a small, watertight connection for 2 sections of pipe.  Make sure slip coupling matches the diameter size, length, and type of your pipes such as PVC or copper.
  • Cut out the right length of pipe by holding the slip coupling up to the leaky spot and mark both ends to not go beyond the ends of the coupling.
  • Cut out the leaky pipe between the inside of the marked lines with a pipe cutter or hacksaw.
  • Deburr both sides of the cut pipe to prevent future leaks with a deburring tool.
  • Slide the slip couplings in between the ends of the cut pipe. Tighten per package instructions.

2. Epoxy Putty (temporary fix)

  • Using latex gloves, mix plumbing epoxy putty by hand.
  • Wrap ½” thick putty around the leaking area on pipe & taper the edges.
  • Putty should set for 5-10 minutes before water gets turned on.

3. Turn off the water supply

  • Locate your main water supply and turn it off to prevent further water damage.
  • Drain the faucets connected to the pipe starting with the lowest ones in your home.
  • Once all pipes are drained, dry off the leaking pipe, keep a towel or bucket underneath it, and fix it.

4. Clamp small leaks (temporary fix)

  • Use a pipe clamp the same size as the leaky pipe ensuring a snug fit.
  • Using the rubber gasket inside the clamp, place it on the leak so it is a tight seal, clamp it, and tighten the bolts provided with the clamp.
Tips on plumbing maintenance
  • Replace mechanical faucets before they get to the point of no return
  • Tighten wall connections & look for rust, buckling, or water drips
  • Replace washers, gaskets, & O-rings regularly (extends the life of the fixture)
  • Check water heater & liner
  • Make sure frost-free hose bib is installed at the spigot
  • Kitchen sink maintenance - periodic (random) water leak checks
  • Insulate your pipes where cold water pipes touch building exterior

Check for peeling paint, mold, & mildew

Dampness may cause the paint on your basement walls to peel. Check those areas for signs of leaks and cracks. Foundation settling may also be the problem.

Every homeowner can spell one of their nightmares with a four letter word: m-o-l-d. Mildew and mold thrive in dark and damp areas and tend to grow well near the source of moisture.

Check for water deposits and water stains

If you find that water is collecting in one location, investigate it for cracks or ways that it is letting water in. Check nearby faucets and toilets to see if they might be leaking water.
Red water stains anywhere on your walls is a sure sign you may have found your leaking water source.

Spalling - Chunks of Concrete Falling Off Wall

What causes chunks of concrete to fall off?

If you are finding chunks of concrete falling off your basement wall, moisture is penetrating the wall and is a sign there is a problem with the steel rebar within the wall or the anchor bolts embedded in the wall. Rebar will rust over time and deteriorate the structural strength of a wall.

What causes a basement to leak or flood?

There are many reasons why a basement may flood, including:

  • Cracked cinder blocks/poured wall slabs
  • Leaking basement windows & hatchway entrances
  • Gutter debris & improper downspout installation
  • Sump pump & drainage tile failure
  • Main water line/home plumbing; hot water tank
  • Condensation
  • Foundation Issues
  • Cracked concrete floor
  • Floor drains
  • Wall-floor joint
  • Inadequate Basement Sealing

Let’s break these down into where the water might be, what to look for, and possible solutions to mitigate the issue.

Cracked Cinder Blocks or Poured Wall Slabs

What are the different kinds of basement wall cracks?
  • Horizontal
  • Vertical
  • Diagonal
  • Stair-stepped
What are the causes of basement wall cracks?

There are several reasons why basement cracks happen. Loads or pressures pushing on the basement walls generally cause basement cracks and leaks to happen.  Foundation issues, hydrostatic pressure, or concrete shrinkage are causes for cracks to occur.

Foundation issues may be from it settling or moving. Hydrostatic pressures are caused by saturated soil or high water tables. The concrete curing process is the most common source of basement wall cracks and are usually cosmetic.

What causes horizontal cracks in basement walls?

Horizontal cracks are generally not caused by settling or the footing heaving, but by lateral pressure on the wall. It is common for clay soils to experience horizontal cracks.

There are five causes of horizontal wall cracks, which include:

1. Back-filling soil directly after basement being poured

  • Soil filled before full structural strength reached
  • Should wait 28 days
  • Causes lateral stress
  • Compaction too soon: Loose compaction holds more water and increases hydrostatic pressure

2. Weight of vehicles/equipment near basement wall

  • Puts downward pressure on soil
  • Adds to existing lateral pressure
  • Cracks occur top ⅓ of basement wall

3. Soil Loading Issues

  • Weight of soil against wall. Wall is bowed or tilting inward. Greatest pressure at bottom ⅓ .

4. Hydrostatic Pressure/Moisture Loading

  • Main cause for basement leaks
  • Key factor in creating lateral pressure
  • High water tables
  • Poor drainage
  • Sewer/water line leaks

5. Frost-Heaving & Ice Lenses

  • Saturated soil will expand when freezes
  • May crack, tilt, or bow from pressure
  • Rare vertical cracks in basement corner areas

Horizontal cracks in cinder block basement walls have similar reasons to poured concrete walls, but there are several things to watch for: horizontal cracks in the mid 1/3 area, cracks >⅛” and bowed, and if the bowing is >⅜” (structural problems).

Other horizontal cracks that need further inspection are ones near the bottom, at the grout line above the first few bottom courses, or cracks that run parallel to horizontal cracks.

Vertical Cracks

What causes vertical cracks in basement walls?

Vertical cracks are commonly seen on basement walls. A few of them are not related to structural integrity:

  1. Shrinkage cracks
    -Excess water in concrete mix
  2. Contraction joints
    -Straight vertical control joint
    -Newer poured walls
    -Put there for contraction purposes
    -Controlled crack
  3. Cold Joints
    -Where two different batches poured
    -Proper waterproofing needed
    -Looks like a crack, not one

Vertical cracks that may need further inspection or may be a source of leaking water occur from a footing that may be cracked, tilted, or rotating. The crack may run partially up the wall. The wall may be offset on either side of the crack.

Vertical cracks that are wider at the top than the bottom may happen from a cracked footing and differential settling. The excessive force is causing the wall to break away.

Vertical cracks occurring at the basement wall corner may be from excessive water build-up from improperly placed gutter downspouts alongside a combination of the water thawing and freezing. Reposition the gutter downspouts to prevent this from happening.

Stair Stepped & Diagonal Cracks

What causes stair-stepped or diagonal cracks on basement walls?

Diagonal cracks are usually from shifting soils, premature backfilling, settlement, expansive soils, or even footing compaction issues.

What are the different types of diagonal cracks in basement walls?
  • Runs from top of wall down to the bottom
  • From lateral pressure on top/midway section
  • Wall might tilt inward at top
  • May have damaged first-floor sill plate
  • Exterior framed house wall not sitting squarely

Basement Window & Door Corner Cracks

How do basement windows and doors get cracks?

Typically, window and door corner cracks occur from shrinkage issues. Other causes include stress concentrated on those areas from the shifting or movement of footings and/or basement walls.

If you can enter your basement through the exterior of your house, the stairs leading down to the entrance may be a perfect way for water to leak into your basement.

Gutter Debris & Improper Downspout Installation

How do gutters or downspouts cause basement leaking?

Nothing promotes pooling and standing water like aging gutters or a poorly installed gutter system. All that water accumulates around your home’s foundation and eventually ends up in your basement.

Inspect your gutters and downspouts to make sure you have at least four feet of clearance, gutters are cleaned and replace/install new gutters properly.

Failing Sump Pumps: How do sump pumps keep water out of your basement?

Usually, a sump pump and a perimeter drain system work cohesively when there is a leak from a floor crack. Sump pump pits are deeper than your floor and work by pumping out extra or flooding water out to the drainage system, where it collects the water and drains the water away from your home before it even reaches your floor.
In some circumstances running a lateral drainage line from the crack to the sump pump will help solve the immediate flooding problem.

How does a sump pump cause basement water leaks?

Sump pumps are a necessary system for removing excess water from a basement. But when they fail, water can back up into the basement and cause flooding.

What causes a sump pump to fail?

There are multiple reasons why sump pumps fail and it is important to do your due diligence to prevent these from occurring:

  • Losing power
  • Dead batteries for a back-up system
  • The high water alarm stopped working
  • The motor running the pump breaks
  • The float is ineffective
  • Inadequate size
Tips on preventing sump pump failure
  • Check power source  
    -breakers on pump outlets can trip shutting off the sump pump w/o knowing
  • Test the sump pump  
    -fill basin with some water & make sure it works
  • Inspect & clean grate of debris
  • Make sure it is plugged in & works
  • Check drain pipes
  • Make sure the sump pump is level

Weeping Tile Failure

How does a drain tile system failure cause water to leak into a basement?

Inadequate drainage can feed back through your basement floors and walls. This will ultimately result in basement leaks and water damage. Problems that may arise, wreaking havoc on your drain tile, are clogs from silt, deterioration of the home parting or the soil surrounding the home’s foundation being overly saturated - which takes several months to dry up.

Leaking Main Water Line/Home Plumbing Issues

What causes the main water lines to leak water into the basement?

Leaks in the main water lines may occur from underground freezing and thawing, soil erosion, natural wear and tear and rodents. Main water lines carry a large amount of water so it is important to investigate and fix as soon as possible to prevent significant water damage.

What causes leaks in a home’s plumbing system?
  • broken seals
  • clogging in the pipes
  • corrosion
  • damaged pipe joints
  • excessive water pressure
  • loose water connectors
  • extreme weather changes such as freezing causing pipes to burst

Failing Hot Water Tank

What causes the hot water tank to flood the basement?

Hot water heaters last approximately seven years and when they fail, the water leaks right on the basement floor.

If there is a plastic ring around the unit, the ring will drain into the waterproofing system, if there is one, and then to the sump pump. If there is not a waterproofing system in place, a small water sensor can be installed within the ring so that when or if a water heater floods out, the alarm will sound off notifying the owner of the leak.

Condensation Problems

How does condensation cause a wet basement?

Warm air holds moisture and in the summer, air humidity increases, causing general dampness in basements. Condensation can often be confused with runoff or subsurface water.

How can I tell if it is condensation or subsurface water?

Tape a piece of foil over damp spots and check the next day. If moisture is on the outer side: condensation. If moisture is on the underside, water is leaking in from the outside.

How do you prevent condensation?

There are a few steps you can take to reduce condensation:

  • Install a dehumidifier near easy drainage
  • Open windows & use fans
  • Apply a waterproof coating
  • Insulate cold-water pipes with foam insulation
  • Check for dryer duct leaks
  • Foundation vents
  • Crawl Spaces - cover ground with 6-mil polyethylene plastic sheeting

Foundation Problems

What foundation issues cause water leaking into the basement?

A common basement leak issue is due to poor grading around the foundation exterior. In this instance, the ground is sloping toward the foundation preventing proper water drainage.
A good way to see if grading is a problem, take a walk around the property outside to see if there is any water accumulation or if the ground level is sloping toward the foundation. Add soil to low spots. Soil and interlock brick settle over time and should be inspected annually.

Cracked Concrete Basement Floor

The loose soil back-filled around the walls and under the floor absorbs and holds water and when it rains, the water builds up and enters a home through the cracks in the floor.

What causes concrete basement floors to crack?

Damage from tree roots, earth movement, settling foundations, and poor construction can crack basement concrete floors. These cracks are quite normal. Some cracks are worrisome and will need further inspection and need to be fixed:

  • Cracks with heaving
    -The soil beneath the basement floor is expanding
  • Cracks ½” or larger need to be leveled
    -PolyLevel permanently lifts & stabilizes a sinking concrete slab
    -Penny-sized holes drilled into the slab
    -A structural-grade polymer is injected
    -Polyurethane material expands, lifting & leveling the slab
  • Seal ⅛” or wider cracks
    -Prevents radon from seeping in
    -Reduces moisture & soil smells
How do you stop the water from leaking through the floor cracks in your basement?

A sump pump and exterior drainage system will keep water from leaking in through basement floor cracks. For more serious floor cracks, a lateral drain can be trenched on the floor and sloped downwards towards the perimeter system. The water will drain out naturally.

Floor Drain Issues

The basement floor drain removes water from below the house and can get clogged up, cause odors, and allow water to back up into the basement.

How does a sewer drain cause water to flood a basement?

Sometimes a sewer pipe bursts and sewage will drain out onto the basement floor. Leaking joints can also allow sewage and water to escape.

If there is a bad odor and the floor is wet, the sewer drain may be the culprit. Grab a snake and feed it down the drain with some water until you have removed the debris.

Wall-Floor (Cove) Joint Problems

The cove joint is where the wall and floor meet and can be a source of leaking water into a basement.

What problems happen with cove joints that cause water to leak into a basement?

Many times, hydrostatic pressure, which happens when the water table rises after rain or snowmelt. The weight of water in the ground (8 pounds per gallon) forces water under the footing and into the basement.

These cracks should be sealed to keep out moisture and water because, over time, this can create structural integrity problems. Interior drain tile systems work the best along with an exterior waterproofing system.

Inadequate Basement Sealing

Many water leaks and basement flooding can be prevented by investing in a high-quality basement waterproofing sealer. If this was never done when the house was built or done improperly a wet basement is inevitable.

Can a basement be sealed after the fact?

Yes. It is important to remove any paint, dirt, mold, and efflorescence before applying a waterproofing sealer and make sure to follow the manufacturer’s instructions so that it is applied correctly and effectively.

Make sure to repair all cracks, plumbing system issues, sump pump problems, main water line leaks, and any other issues that are causing water to seep into the basement before applying the sealer.


Most basement cracks result from moisture issues and improper drainage. The goal is to keep the least amount of moisture near the basement wall and foundation.

How to prevent water leaks:
  • Soil should slope away from the home
  • Should drop 6 inches in 10 feet
  • No areas with standing water
  • Channel water away from the house around patios, walks, and driveway
  • Maintain gutters & downspouts - should carry water a great distance from the basement wall
  • Maintain sprinkler system - avoid overwatering. Also check for leaking sprinkler pipes & standing water.

Schedule an annual inspection of anything that affects keeping your basement dry to prevent any future water damage. This will save you money and the hassle of dealing with a wet basement.

At Christian Brothers Construction, we specialize in foundation repair and basement leaks. Whether you are in need of repair because of damage that has already occurred, or you're looking to prevent water in your basement, we would be honored to serve you. Give us a call today for a comprehensive assessment to plan for water drainage and management. What are you waiting for?!