Louisiana well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Louisiana county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 64 counties
- St. Tammany ParishWell users 49,900Arsenic about 1 in 100Nitrate 0.0 mg/L
- Tangipahoa ParishWell users 37,900Arsenic about 1 in 100Nitrate 0.1 mg/L
- Vermilion ParishWell users 27,100Arsenic about 3 in 100Nitrate 0.0 mg/L
- Calcasieu ParishWell users 26,200Arsenic about 1 in 100Nitrate 0.0 mg/L
- Lafayette ParishWell users 23,200Arsenic about 2 in 100Nitrate 0.1 mg/L
- Caddo ParishWell users 21,800Arsenic about 2 in 100Nitrate 0.0 mg/L
- Livingston ParishWell users 21,700Arsenic about 2 in 100Nitrate 0.0 mg/L
- Washington ParishWell users 21,300Arsenic about 2 in 100Nitrate 0.3 mg/L
- Ascension ParishWell users 19,700Arsenic about 2 in 100Nitrate 0.0 mg/L
- Vernon ParishWell users 18,500Arsenic about 1 in 100Nitrate 0.1 mg/L
- Acadia ParishWell users 18,400Arsenic about 3 in 100Nitrate 0.0 mg/L
- Bossier ParishWell users 16,100Arsenic about 2 in 100Nitrate 0.0 mg/L
- Iberia ParishWell users 11,200Arsenic about 2 in 100Nitrate 0.0 mg/L
- Sabine ParishWell users 10,400Arsenic about 1 in 100Nitrate 0.0 mg/L
- Beauregard ParishWell users 9,400Arsenic about 1 in 100Nitrate 0.1 mg/L
- De Soto ParishWell users 8,700Arsenic about 2 in 100Nitrate 0.1 mg/L
- St. Landry ParishWell users 8,500Arsenic about 2 in 100Nitrate 0.0 mg/L
- Franklin ParishWell users 8,200Arsenic about 2 in 100Nitrate 0.4 mg/L
- Rapides ParishWell users 7,400Arsenic about 2 in 100Nitrate 0.1 mg/L
- Ouachita ParishWell users 6,700Arsenic about 2 in 100Nitrate 0.1 mg/L
- St. Helena ParishWell users 6,600Arsenic about 2 in 100Nitrate 0.1 mg/L
- St. Martin ParishWell users 6,500Arsenic about 1 in 100Nitrate 0.0 mg/L
- Richland ParishWell users 6,100Arsenic about 2 in 100Nitrate 0.5 mg/L
- Jefferson Davis ParishWell users 5,500Arsenic about 1 in 100Nitrate 0.0 mg/L
- Natchitoches ParishWell users 5,200Arsenic about 1 in 100Nitrate 0.2 mg/L
- Webster ParishWell users 4,800Arsenic about 1 in 100Nitrate 0.1 mg/L
- Evangeline ParishWell users 4,100Arsenic about 1 in 100Nitrate 0.0 mg/L
- Bienville ParishWell users 3,700Arsenic about 1 in 100Nitrate 0.1 mg/L
- Allen ParishWell users 3,500Arsenic about 1 in 100Nitrate 0.1 mg/L
- Claiborne ParishWell users 3,100Arsenic about 1 in 100Nitrate 0.0 mg/L
- Grant ParishWell users 3,100Arsenic about 3 in 100Nitrate 0.5 mg/L
- East Feliciana ParishWell users 2,900Arsenic about 3 in 100Nitrate 0.1 mg/L
- Red River ParishWell users 2,700Arsenic about 1 in 100Nitrate 0.2 mg/L
- Pointe Coupee ParishWell users 2,600Arsenic about 5 in 100Nitrate 0.0 mg/L
- East Baton Rouge ParishWell users 2,500Arsenic about 2 in 100Nitrate 0.0 mg/L
- Morehouse ParishWell users 2,400Arsenic about 2 in 100Nitrate 0.1 mg/L
- Union ParishWell users 2,300Arsenic about 1 in 100Nitrate 0.1 mg/L
- Winn ParishWell users 2,300Arsenic about 2 in 100Nitrate 0.0 mg/L
- Lincoln ParishWell users 2,100Arsenic about 1 in 100Nitrate 0.1 mg/L
- Iberville ParishWell users 2,000Arsenic about 2 in 100Nitrate 0.0 mg/L
- Avoyelles ParishWell users 2,000Arsenic about 2 in 100Nitrate 0.1 mg/L
- Jackson ParishWell users 1,900Arsenic about 1 in 100Nitrate 0.1 mg/L
- Orleans ParishWell users 1,300Arsenic about 2 in 100Nitrate 0.0 mg/L
- Cameron ParishWell users 1,100Arsenic about 2 in 100Nitrate 0.0 mg/L
- Catahoula ParishWell users 1,100Arsenic about 2 in 100Nitrate 0.0 mg/L
- St. Mary ParishWell users 890Arsenic about 2 in 100Nitrate 0.0 mg/L
- West Carroll ParishWell users 860Arsenic about 2 in 100Nitrate 0.1 mg/L
- Concordia ParishWell users 820Arsenic about 2 in 100Nitrate 0.0 mg/L
- LaSalle ParishWell users 670Arsenic about 3 in 100Nitrate 0.2 mg/L
- Caldwell ParishWell users 600Arsenic about 2 in 100Nitrate 0.1 mg/L
- West Feliciana ParishWell users 590Arsenic about 4 in 100Nitrate 0.1 mg/L
- St. John the Baptist ParishWell users 500Arsenic about 2 in 100Nitrate 0.0 mg/L
- West Baton Rouge ParishWell users 440Arsenic about 3 in 100Nitrate 0.0 mg/L
- St. Charles ParishWell users 350Arsenic about 2 in 100Nitrate 0.0 mg/L
- Jefferson ParishWell users 320Arsenic about 2 in 100Nitrate 0.0 mg/L
- Madison ParishWell users 290Arsenic about 4 in 100Nitrate 0.0 mg/L
- Assumption ParishWell users 260Arsenic about 2 in 100Nitrate 0.0 mg/L
- Tensas ParishWell users 230Arsenic about 2 in 100Nitrate 0.0 mg/L
- East Carroll ParishWell users 170Arsenic about 3 in 100Nitrate 0.0 mg/L
- Terrebonne ParishWell users 140Arsenic about 3 in 100Nitrate 0.0 mg/L
- St. James ParishWell users 110Arsenic about 3 in 100Nitrate 0.0 mg/L
- Plaquemines ParishWell users 100Arsenic about 2 in 100Nitrate 0.0 mg/L
- St. Bernard ParishWell users 30Arsenic about 2 in 100Nitrate 0.0 mg/L
- Lafourche ParishWell users 10Arsenic about 4 in 100Nitrate 0.0 mg/L
Each mark = 1 in 100 well users the model places above 10 µg/L arsenic (scale 0–10)10 mg/L nitrate: the federal limit (MCL) for public systems
- These figures describe the area, not your well. Only a lab test shows what’s in your water.
- CDC says the Well Water Index figures “do not describe risk to individual wells.” (CDC Tracking Network)
- The arsenic model is better at spotting low-arsenic areas than at confirming high ones.
- Well-user counts are 2010 USGS estimates; tract values are averages over each census tract.
- Total coliform bacteriaEvery year
- NitrateEvery year
- Total dissolved solidsEvery year
- pHEvery year
- ArsenicAsk your local health department
EPA: Private Drinking Water Wells · CDC: Guidelines for Testing Well Water
Use a state-certified lab
Louisiana Department of Health lists the laboratories certified to test drinking water in Louisiana.
Screening tells you if something is worth a closer look
A lab result is the number you can act on.
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Lab-certified results
ETR Labs Basic Water Quality Test Kit
ETR Laboratories
50+ substances, including lead, copper, arsenic, nitrate, hardness and coliform bacteria
- Analyzed by Environmental Testing and Research Laboratories (ETR Labs), Leominster, MA · ISO/IEC 17025:2017, ANAB certificate AT-2638
- Turnaround: 2–4 business days after the lab receives it
What it can't tell you: It does not test PFAS, and not every result on the panel falls under the lab's accredited scope.
Screening: quick check, not lab-grade
Watersafe Drinking Water Test Kit
Silver Lake Research
Lead, bacteria, nitrate, copper, iron, chlorine, hardness and pH
- Turnaround: Minutes; the bacteria test can take up to 48 hours
What it can't tell you: Each test gives a yes/no or a rough range, not a lab number, and it cannot detect PFAS or arsenic.
A mail-in kit’s lab is accredited (ISO/IEC 17025) but may not be certified by your state. For a home sale, a loan, or a health-department follow-up, use a state-certified lab.
Louisiana well water
Sources: CDC Well Water Index (2024) · USGS arsenic and nitrate models · USGS domestic well populations · EPA and CDC testing guidance. Data last updated 2026-10-08. All sources →
How many people use private wells in Louisiana?
About 461,100 people across 64 Louisiana counties, by the USGS 2010 estimate. USGS models place about 8,000 of them in areas where wells are likely to be above the 10 µg/L arsenic limit. These are area estimates, not well results.
Are private wells regulated in Louisiana?
The quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments and laws. (EPA) Testing and treatment are the owner's responsibility.
Where can I get my well tested in Louisiana?
Louisiana Department of Health keeps the list of laboratories certified to test drinking water in Louisiana. Only use laboratories that are certified to do drinking water testing. (EPA)