Well water in Zapata County, Texas
No public well test results have been compiled for Zapata County yet. The USGS national arsenic model estimates that 4% of the 592 people on private wells there draw water with arsenic above 10 ug/L, the EPA limit, based on geology, well depth and land use rather than local tests.
The strongest signal is coliform bacteria: Recommended for every private well, every year, too few samples to carry the headline but first on the test list below.
104 test results across 10 contaminants from at least 8 wells, 1961 to 2005; fluoride has the most at 12. 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.
An estimated 592 people in Zapata County get their drinking water from a private well, per USGS 2015 county water use. That is about 4% of residents.
Separately, the USGS national arsenic model estimates that 4% of the 592 people on private wells in Zapata County draw water above 10 ug/L (the model's range is 3% to 5%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Zapata 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 |
|---|---|---|---|---|---|---|
| Fluoride 1961 to 2005 | 12 | 92% | 0.52 | 2.26 | 4 mg/L EPA limit | |
| Nitrate 1994 to 2005 | 10 | 20% | 0 | 0.037 | 10 mg/L EPA limit | |
| Copper 1994 to 2005 | 10 | 20% | 0 | 0.005 | 1.3 mg/L EPA limit | |
| Lead 1994 to 2005 | 10 | 0% | 0 | 0 | 15 ug/L EPA limit | |
| Arsenic 1994 to 2005 | 10 | 10% | 0 | 3.55 | 10 ug/L EPA limit | |
| Chloride 1961 to 2005 | no limit | 12 | 100% | 464 | 2,768 | 250 mg/L nuisance level |
| Sodium 1961 to 2005 | no limit | 12 | 100% | 531 | 2,330 | 20 mg/L health guideline |
| Iron 1961 to 2005 | no limit | 11 | 91% | 272 | 2,850 | 300 ug/L nuisance level |
| Manganese 1994 to 2005 | no limit | 10 | 90% | 12.3 | 45.2 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Gross alpha (7).
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
Among contaminants with a federal limit, no tested sample in Zapata County came back above it. That is reassuring, but sampling is uneven: wells that were never tested are not in this data.
Chloride, Iron, and Manganese 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 Zapata County
- 1Coliform bacteriaRecommended for every private well, every year.
- 2NitrateRecommended for every private well, especially near farms or septic systems.
- 3ChlorideDetected in 100% of local samples.
- 4FluorideDetected in 92% of local samples.
- 5IronDetected in 91% of local samples.
- 6ManganeseDetected in 90% of local samples.
- 7Volatile organic compounds (VOCs)7 leaking underground storage tank sites on record locally.
Test your Zapata County well for coliform bacteria, nitrate and chloride
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 Zapata County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Zapata County
Texas coastal uplands 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 Zapata County
TCEQ records 7 leaking underground storage tank sites in Zapata County, among 11 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.
- 7
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 4
- lined landfills and transfer facilities
Treatment that fits the local profile
Chloride
Point-of-use reverse osmosis; Distillation
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
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 chloride
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For iron
Iron and manganese oxidizing filter
whole-house, at the point of entry, about $1,800
Air-injection or greensand media; fixes staining at the source.
Free, no obligation
Get on the list for a free in-home water test in Zapata County
No water treatment company serves Zapata 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 Zapata County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Zapata County?
Arsenic was detected in 10% of 10 public well samples in Zapata County, and 0% 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 often should I test a private well in Zapata 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 Zapata 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
- Texas Water Development Board Groundwater Database: 104 samples in Zapata 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 592 people on private wells in Zapata 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: 11 regulated sites located in Zapata 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.