Original data
In most US cities, the basement floor is below the water table
A full basement floor sits about 7 feet down. We used USDA soil-survey data to find how shallow the water table rises in a typical year across 179 cities. In every one of them, at its seasonal high, the groundwater comes up past where a basement floor would be.
The water table's seasonal high has a median depth of just 1.8 feet.
Across 179 cities the median is 1.8 feet, and in 79 the water table reaches the surface at its peak. All 179 rise above a typical basement floor. A basement in these cities is dug straight into the zone the seasonal water table occupies.
Own a home with a basement? This is why interior drainage and a sump pump are so common: when the water table rises after rain or snowmelt, it pushes up against the slab and in at the wall-floor joint. Grading and gutters help, but they do not lower groundwater. That is the sump pump's job.
Covering flooding or housing? This is soil-survey groundwater data mapped to the cities people search for, alongside our FEMA claims analysis. Together they make the same point from two sources: basement water is a groundwater problem, and the flood map is looking at rivers.
The 21 cities with no water-table rating
SSURGO does not rate a shallow water table in 21 of our cities, and they are not scattered: they are the arid West and the Texas clay belt, places like Denver, Colorado Springs, Austin, and Fort Worth. There the ground is dry or the soil is deep clay, and the basement threat is not rising groundwater but the clay itself swelling and shrinking. That failure mode is in our per-city soil data as shrink-swell, not here.
Methodology
Source is USDA NRCS SSURGO via Soil Data Access. For each city we sampled 17 points on two rings around the centre and read wtdepannmin, the shallowest the water table rises in a typical year, area weighted per map unit. We report the median across the points that carry a rating.
This is an annual minimum, a seasonal high, not a level the water holds year round. The water table rises to this depth; it does not sit there. And these are soil-survey estimates, not a reading of your lot.
"Reaches the basement floor" means shallower than 213 cm (7 ft), a typical full-basement floor depth. Shallower slabs and crawl spaces meet the water table sooner still. Cities with fewer than 3 rated points are counted in the totals but left out of the ranking, where a median would be one or two probes.
Free to cite or reproduce with a link to this page.
Where the water table rises closest to the surface
152 cities, ranked by how shallow the seasonal high rises. A fuller bar means groundwater closer to the surface, and less dry soil between it and a basement floor.
Using this data
The method is above and the source is public, so the analysis is reproducible. Cite this page. Per-city figures and the harvester are available on request. Our flood claims and permit fee datasets are alongside it.