Well water in Harris County, Texas
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Testing recommended
tested well samples in Harris County exceeded the EPA limit for arsenic (10 ug/L), based on public data from USGS Water Quality Portal and Texas Water Development Board Groundwater Database.
The strongest signal is PFOS: 22% of 27 local samples were above the limit, too few samples to carry the headline but first on the test list below.
3,652 test results across 16 contaminants from at least 293 wells, 1933 to 2025; sodium has the most at 462. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
TWDB samples an ambient monitoring network of wells on a rotation, so these describe aquifers, not a survey of homeowners' tests. In that targeted sampling, 22% of 27 PFOS results in Harris County were above the EPA limit of 4 ng/L. In that targeted sampling, 19% of 27 PFOA results in Harris County were above the EPA limit of 4 ng/L.
An estimated 45,985 people in Harris County get their drinking water from a private well, per USGS 2015 county water use. That is about 1% of residents.
Separately, the USGS national arsenic model estimates that 14% of the 45,985 people on private wells in Harris County draw water above 10 ug/L (the model's range is 10% to 20%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Harris County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| PFOS 2024 to 2025 | 27 | 48% | 0 | 170 | 4 ng/L EPA limit | |
| PFOA 2024 to 2025 | 27 | 26% | 0 | 670 | 4 ng/L EPA limit | |
| Arsenic 1984 to 2025 | 346 | 95% | 2 | 33.5 | 10 ug/L EPA limit | |
| Nitrate 1974 to 2025 | 366 | 74% | 0.2 | 85.1 | 10 mg/L EPA limit | |
| E. coli 2002 to 2014 | 28 | 4% | 0 | 2 | 0 MPN/100mL EPA limit | |
| Uranium 1984 to 2025 | 322 | 97% | 1.47 | 44.5 | 30 ug/L EPA limit | |
| Fluoride 1939 to 2025 | 447 | 96% | 0.22 | 3.7 | 4 mg/L EPA limit | |
| Radium (226 + 228) 1984 to 2016 | 277 | 96% | 0.62 | 4.9 | 5 pCi/L EPA limit | |
| Lead 1984 to 2025 | 197 | 56% | 0.018 | 6.04 | 15 ug/L EPA limit | |
| Copper 1984 to 2025 | 196 | 71% | 0.001 | 0.042 | 1.3 mg/L EPA limit | |
| Sodium 1933 to 2025 | no limit | 462 | 100% | 46.4 | 1,400 | 20 mg/L health guideline |
| Iron 1933 to 2025 | no limit | 425 | 78% | 10.5 | 9,500 | 300 ug/L nuisance level |
| Manganese 1965 to 2025 | no limit | 378 | 87% | 5.46 | 5,580 | 300 ug/L health guideline |
| Radon 2002 to 2016 | no limit | 86 | 100% | 635 | 2,510 | 2,000 pCi/L health guideline |
| Chloride 1933 to 2013 | no limit | 66 | 100% | 39.7 | 459 | 250 mg/L nuisance level |
Sampled fewer than 10 times, too few to summarize: Gross alpha (2).
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Fluoride | 0%128 samples | 0%84 samples | 0%208 samples | 0%27 samples |
| Nitrate | 0%94 samples | 11%118 samples | 1%100 samples | 11%54 samples |
| Arsenic | 0%22 samples | 1%89 samples | 9%208 samples | 4%27 samples |
| Uranium | n/a | 1%82 samples | 2%208 samples | 0%27 samples |
| Radium (226 + 228) | n/a | 0%64 samples | 0%208 samples | n/a |
| Lead | 0%38 samples | 0%84 samples | 0%48 samples | 0%27 samples |
Nitrate above the limit in Harris County rose from 1% of 100 samples in the 2010s to 11% of 54 in the 2020s.
Arsenic above the limit in Harris County fell from 9% of 208 samples in the 2010s to 4% of 27 in the 2020s.
Fluoride, uranium, radium (226 + 228), lead have held within a few points between the two most recent periods with enough samples.
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
The contaminants most often above their limit here are pfos (22% of 27 samples), pfoa (19% of 27 samples), and arsenic (6% of 346 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Iron, Manganese, and Chloride are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Harris County
- 1PFOS22% of 27 local samples were above the limit.
- 2PFOA19% of 27 local samples were above the limit.
- 3Arsenic6% of 346 local samples were above the limit.
- 4Nitrate5% of 366 local samples were above the limit.
- 5E. coli4% of 28 local samples were above the limit.
- 6Uranium2% of 322 local samples were above the limit.
- 7RadonMedian local reading is 635 pCi/L.
- 8Volatile organic compounds (VOCs)4,278 leaking underground storage tank sites on record locally.
- 9Metals panel25 hazardous waste sites on record locally.
Test your Harris County well for PFOS, PFOA and arsenic
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in Texas: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Harris County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Harris County
Coastal lowlands aquifer system
Semiconsolidated sand. Coastal plain sands like these give steady yields at moderate depth. Salt water and sodium are the usual issues near the coast, and nitrate where the water table is shallow; arsenic and radon from bedrock are less common.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Texas
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- Private Wells, Texas Groundwater Protection Committee
- Environmental Laboratory (NELAP) Accreditation, TCEQ
Contamination sources on record in Harris County
TCEQ records 4,278 leaking underground storage tank sites and 25 hazardous waste sites in Harris County, among 4,514 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 4,278
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 25
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 211
- lined landfills and transfer facilities
Treatment that fits the local profile
PFOS
Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
PFOA
Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
E. coli
Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For PFOS
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For PFOS
Whole-house PFAS carbon system
whole-house, at the point of entry, about $3,000
Granular activated carbon certified to NSF/ANSI 53 for PFOA and PFOS; replace media on schedule.
For PFOS
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For PFOA
Aquasana Claryum 3-Stage under-sink filter
under-sink or countertop, about $175
Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.
For PFOA
Aquasana HealthShield whole-house filter
whole-house, at the point of entry, about $2,099
Whole-house carbon system the maker certifies to reduce PFAS (PFOA and PFOS) and VOCs at every tap; a UV option adds bacteria protection.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
Free, no obligation
Get on the list for a free in-home water test in Harris County
No water treatment company serves Harris County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Harris County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Harris County?
Arsenic was detected in 95% of 346 public well samples in Harris County, and 6% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Harris County?
The median radon level across 86 public samples in Harris County was 635 pCi/L, with a high of 2,510 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Harris County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties near Harris County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Texas dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 3,454 samples in Harris County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- Texas Water Development Board Groundwater Database: 198 samples in Harris County. Water quality samples from the Texas Water Development Board Groundwater Database, collected by TWDB, groundwater conservation districts and cooperators. Retrieved September 9, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 45,985 people on private wells in Harris County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- TCEQ regulated sites: 4,514 regulated sites located in Harris County. Leaking petroleum storage tank sites, state Superfund sites and municipal solid waste landfills from the Texas Commission on Environmental Quality. Retrieved September 9, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.