San Antonio, Texas

Inside San Antonio's city limits, shrink-swell clay limits houses without basements on 61% of mapped land, higher than 66% of Texas cities. A shallow water table limits basements on under 1%.

That clay share is above Bexar County's 51%. FEMA's flood data list 235 flood losses since 2016 in the 50 ZIP codes overlapping the city. Of its 612,901 homes, 43% were built before 1980; the median dates from 1985.

Data as of September 22, 2026 · sources · in Bexar County

61%

expansive clay: shrink-swell limits slab homes

<1%

high water table: limits basements

235

flood losses since 2016 in 50 overlapping ZIPs

43%

of homes built before 1980

Soil under San Antonio city limits

Expansive clay (limits slab homes)	60.6%
High water table (limits basements)	under 0.1%
Septic fields very limited	83.1%
Clay swell (LEP, by area)	7.5%
High-swell land (LEP 6%+)	51.6%
Mapped soil	328,254 acres

Soil series	Share here	Series nationally: expansive clay
Eckrant	16%	8%
Houston Black	14%	91%
Lewisville	13%	n/a
Branyon	9%	92%
Sunev	5%	n/a
Austin	4%	93%

San Antonio city limits inside Bexar County, shaded by the city's expansive clay share.under 10%10-25%25-40%40-60%60%+

How we count

What the numbers mean here

Clay swell averages a linear extensibility of 7.5% by land area here, and 52% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 61% of the mapped land.

Clay shrinks as it dries: 60.7% of Bexar County is in drought on the latest map, and 61% of San Antonio's mapped land has shrink-swell clay.

USDA rates 83% of the land very limited for septic absorption fields.

Drought in Bexar County

60.7% of Bexar County is in drought (D1 or worse) on the September 22, 2026 map. County detail.

September 30, 2025Share of area in drought, weeklySeptember 22, 2026

Flood losses by ZIP code

FEMA flood records since 2016 in the ZIP codes that overlap San Antonio. ZIP areas reach past city limits.

ZIP	Share of city land	Flood losses	Paid
78023	5%	8	$255,650
78223	4%	2	$7,160
78221	3%	10	$6,906
78258	3%	6	$111,585
78224	3%	4	$15,305
78251	3%	4	$19,443
78247	3%	3	$20,071
78259	3%	12	$120,019
78216	3%	7	$43,890
78249	3%	2	$15,782
78219	3%	10	$25,047
78222	3%	2	$51,613
78227	3%	4	$37,068
78257	2%	0	$0
78218	2%	3	$71,640
78228	2%	13	$100,201
78211	2%	3	$191,667
78217	2%	4	$21,025
78230	2%	9	$5,804
78240	2%	8	$97,841
78250	2%	16	$501,744
78233	2%	9	$249,318
78214	2%	2	$3,133
78232	2%	7	$96,982
78238	2%	11	$251,324
78242	2%	2	$21,105
78207	2%	2	$0
78210	2%	2	$0
78220	1%	0	$0
78237	1%	5	$7,643
78256	1%	2	$8,753
78201	1%	11	$127,629
78209	1%	12	$35,941
78212	1%	13	$111,841
78229	1%	2	$33,075
78254	1%	3	$96,560
78213	1%	7	$76,921
78226	1%	0	$0
78234	1%	0	$0
78248	1%	2	$0
78244	1%	1	$0
78202	1%	2	$0
78204	1%	0	$0
78225	under 1%	1	$1,793
78235	under 1%	0	$0
78203	under 1%	0	$0
78231	under 1%	3	$19,262
78205	under 1%	5	$92,653
78208	under 1%	0	$0
78215	under 1%	1	$78,300

Homes in San Antonio

Housing units	612,901
Median year built	1985
Built before 1980	43%
Built 2000 or later	31%
Owner-occupied	52%
Median value, owner-occupied	$235,700
Single-family detached	59%

Nearby cities

Place	Distance	Expansive clay	High water table
Olmos Park	2 mi	65%	0%
Balcones Heights	3 mi	52%	0%
Alamo Heights	4 mi	43%	0%
Castle Hills	4 mi	67%	0%
Terrell Hills	5 mi	74%	0%
Leon Valley	6 mi	64%	0%
Kirby	8 mi	86%	0%
Hill Country Village	9 mi	71%	0%

Sources: USDA SSURGO (August 5, 2026) · US Drought Monitor (September 22, 2026) · FEMA NFIP v3 (September 9, 2026) · Census ACS 2020-2024. Methods · Data status