If your basement is dry most of the year and wet after a hard rain, the water is coming from the surface. That is good news. Groundwater problems mean pumps and interior drains. Surface water problems mean the roof, the downspouts and the first ten feet of dirt around the house, and those are cheaper to fix than anyone selling a waterproofing system will tell you.
Start with where it shows up
| What you see | Most likely source |
|---|---|
| Wet along one wall or in one corner, near a downspout | That downspout, dumping at the foundation |
| Wet along a whole wall under a long gutter run | Gutters overflowing, or the ground sloping toward the house |
| Water in a window well, then inside | The well filling faster than its drain can take, or no drain at all |
| Seeping from the joint where floor meets wall, several places at once | Groundwater pressing on the foundation after days of rain or during snowmelt |
| Coming up through the floor drain | Sewer backup. Not rain, and not a gutter problem |
The first two rows are gutter problems, and a side of the house with no gutter at all is often the one getting wet. The third is half a gutter problem, because most window wells fill from a downspout or an overflowing run nearby. The last two are not, and this page will say so plainly rather than sell you a downspout for a groundwater leak.
How much water a downspout actually moves
A one-inch rain on a 600 square foot roof plane is about 375 gallons. A single downspout carries all of it, and a downspout with no extension drops it in one spot a foot from the wall. That spot is usually the same corner the basement gets wet in, and the soil there has been soaked, dried and soaked again every summer since the house was built, which is why it channels water straight down to the footing.
The Sioux Falls record is 5.67 inches in a day, and a two-inch storm is an ordinary summer afternoon here. Multiply accordingly.
Go outside in the rain
Ten minutes in a steady rain tells you more than an hour of guessing. Look for:
- Water pouring over the front of a gutter, or running down the wall behind it
- A downspout with no extension, or one that ends on a splash block that sends water back toward the house
- Water pooling against the foundation instead of running away from it
- A window well with standing water in it
- A driveway, patio or walk that slopes toward the house
- The sump discharge line ending within a few feet of the foundation, so the pump is recycling its own water
Then look at the corner of the basement that gets wet and match it to what you saw above it. Nine times out of ten the answer is one downspout.
The fixes, cheapest first
Extend the downspouts. Each one should discharge at least 5 feet from the foundation, onto ground that falls away. A rigid or roll-out extension costs about $33 to $40. A splash block alone moves water 1 to 3 feet, which is why houses with splash blocks still get wet basements.
Fix the grading. The building code wants the soil to fall 6 inches in the first 10 feet from the house. Settled backfill along a foundation often slopes the other way. A few yards of clay-heavy fill, not topsoil, packed against the wall and sloped out, is a weekend and a few hundred dollars.
Bury the line. For a downspout that cannot discharge into the yard, or a yard that slopes the wrong way, a solid pipe sloped at least 1/8 inch per foot to a pop-up emitter 10 feet or more out costs $150 to $350 per downspout. In Sioux Falls it needs an overflow tee near the downspout, because the line sits well above the 42-inch frost depth and will freeze. Call 811 at least two business days before digging. Our downspouts and drainage guide has the details.
Deal with the window well. A well needs a drain to the footing tile or a gravel base deep enough to soak away what falls in it, and a cover keeps most of the rain out in the first place. A well with no drain is a bucket against your foundation.
Fix the gutters that started it. If the gutter is overflowing, clean it, and if it still overflows, work through the eight causes. Undersized downspouts are a common one on this list. A 2×3 clears about 600 square feet of roof, and one 3×4 replacing it clears twice that.
Get a free quote for your house
What Sioux Falls will not let you do with the water
Roof runoff and sump water cannot go into the sanitary sewer without the city engineer approving it, and a sump pump cannot be piped to a floor drain. This is not a formality. In June 2024, with the city under a flood warning and the wastewater plant struggling to keep up, Sioux Falls activated its emergency operations center and told residents the single most important thing they could do was check that their sump pumps were not discharging into floor drains. Sewer backups followed anyway.
The other rules: sump water cannot ice a street, alley or sidewalk or run onto a neighbor, sump discharge should land at least 20 feet from the house, and eave pipes cannot drain across a public sidewalk. Regrading inside 100 feet of the regulated floodplain needs a city floodplain permit.
When it is not the gutters
Water seeping from the joint where the floor meets the wall, in several places, days into a wet spell or during the spring melt, is groundwater. The water table has risen above the floor and the foundation is sitting in it. Extensions and grading still help, because they stop adding to it, but the fix is a working sump pump with a backup, and in bad cases an interior drain. That is a different trade and a different budget.
Water rising through the floor drain is the sewer. It is not rain and it is not yours to fix with a shovel. Stop running water in the house and report it. During the 2024 storms the city asked residents to call 211 for suspected backups.
The order to do things in
- Extend every downspout to 5 feet or more
- Regrade the low spots against the foundation
- Cover and drain the window wells
- Bury the lines that cannot discharge into the yard
- Only then price an interior system
Most Sioux Falls basements that leak after rain stop at step one or two. A waterproofing quote that starts at step five without asking about the downspouts is solving the expensive version of your problem.
Questions about water in the basement
Why does my basement only leak when it rains?
Because the water is coming from the surface, not the water table. Rain lands on the roof, leaves the downspouts and soaks in beside the foundation. That is a drainage problem outside, and it is usually cheaper to fix than an interior system.
Can gutters cause water in the basement?
Yes. A 600 square foot roof plane sheds about 375 gallons in a one-inch rain, and a downspout with no extension drops all of it a foot from the wall. Overflowing gutters do the same along the whole eave.
How far should downspouts discharge from the house?
At least 5 feet onto ground that falls away from the house, and 10 feet or more through a buried line. A splash block on its own moves water 1 to 3 feet, which is not enough.
Can I run my sump pump into the floor drain?
No. Sioux Falls code keeps roof and sump water out of the sanitary sewer, and during the June 2024 flooding the city said checking for exactly this was the most important thing homeowners could do.
How much does it cost to fix?
A downspout extension is about $33 to $40. A buried line to a pop-up emitter is $150 to $350 per downspout. Regrading a low spot is usually a few hundred dollars of soil and labor. Interior drain and sump systems start in the thousands, and they are the last step, not the first.
What if water is coming up through the floor drain?
That is the sewer, not rain. Stop using water in the house and report it. During the June 2024 storms the city asked residents to call 211 for suspected sewer backups.
Get a quote
Tell us about the job, with a photo of the downspout nearest the wet corner, and a local gutter contractor will call, text or email to set up a visit. The quote is free.
Related
- Downspouts and drainage, including buried lines and where water can legally go
- Why gutters overflow
- Cleaning and repair cost
- Town by town rules for roof and sump water