Well Water and Septic System Safety in Texas

Texas requires 50 feet between septic tanks and private wells, and 150 feet for drain fields near public wells. Test annually for coliform bacteria and nitrates.

An estimated 1.2 million Texas homes rely on both a private well and a septic system (Texas Water Development Board). When both work properly and are spaced correctly, they coexist safely. But when a septic system fails or setback distances aren't maintained, your well water can become contaminated with bacteria, nitrates, and other pollutants.

This guide covers the distance rules, testing recommendations, and what to do if your well water shows signs of contamination.

How Far Must a Septic System Be from a Well in Texas?

The setback distances between wells and septic systems are designed to give the soil enough distance to filter contaminants before they can reach your drinking water.

TCEQ regulations under 30 TAC Chapter 290 and Chapter 285 set these minimum distances (TCEQ OSSF Program Rules, current as of 2026):

Septic Component	Distance from Private Well	Distance from Public Water Well
Septic tank	50 feet	50 feet
Conventional drain field	50 feet	150 feet
Aerobic spray area	50 feet	150 feet
Drip irrigation field	50 feet	150 feet
Absorption/evapotranspiration bed	50 feet	150 feet

Why the public well distance is greater: Public wells serve more people, so the consequences of contamination are larger. TCEQ applies a wider buffer zone to protect community water supplies.

Additional setback considerations:

• These are horizontal distances measured at the surface, not as the water flows underground
• Some counties require greater distances based on local soil conditions or aquifer vulnerability
• Properties in the Edwards Aquifer recharge zone may have additional restrictions (30 TAC Chapter 213)
• Setback distances apply in all directions, not just downhill

What if your property can't meet these distances? You can apply for a variance through your county's TCEQ-authorized agent. The variance process requires an engineering assessment showing that the proposed setup won't contaminate the well. This is common on smaller lots where space is tight.

How Does Septic Contamination Reach Your Well Water?

Septic contamination reaches wells through groundwater flow when the system fails, is overloaded, or is too close to the well. The most common contaminants are coliform bacteria, E. coli, and nitrates.

Here's how contamination typically happens:

1. Drain field failure. When the drain field is saturated or clogged, wastewater doesn't get adequately filtered by the soil. Pathogens and nutrients can travel through the ground toward the well.
2. Undersized or aging systems. Systems that can't handle the household's wastewater volume push partially treated water into the ground faster than the soil can clean it.
3. Cracked or leaking tank. Raw sewage leaking from a damaged tank can contaminate groundwater directly, bypassing the drain field's filtering process.
4. Flooding. When heavy rains saturate the ground, wastewater from both the drain field and surface runoff can mix with shallow groundwater that feeds your well.
5. Karst geology. In Central Texas, karst limestone features (sinkholes, fractures, caves) allow water to move rapidly underground with minimal filtration. This is why the Edwards Aquifer region has stricter rules.

According to Nathan Glavy, Extension Program Specialist with the Texas A&M Water Resources Institute's OSSF education program, "In karst terrain like the Edwards Plateau, a failing septic system can contaminate a nearby well within days because water moves through limestone fractures with almost no filtration."

Risk factors specific to Texas:

Factor	Risk Level	Where in Texas
Karst limestone terrain	High (rapid groundwater flow)	Hill Country, Edwards Plateau
Shallow water table	Moderate to high	Gulf Coast, East Texas
Heavy clay soil	Lower (slow water movement)	Blackland Prairie, North Texas
Sandy soil	Moderate (fast filtration, less filtering)	Piney Woods, some coastal areas
Expansive clay (cracking)	Moderate (cracks create pathways)	Central Texas, DFW

Soil and geology data from USDA Natural Resources Conservation Service (NRCS) Web Soil Survey and Texas Bureau of Economic Geology.

How Often Should You Test Well Water Near a Septic System?

Test your well water at least once a year for coliform bacteria and nitrates. Test more frequently (every 3 to 6 months) if you've had a positive result, if your well is close to the setback minimum, or after flooding.

Test	What It Detects	Frequency	Approximate Cost
Total coliform bacteria	Indicator of potential fecal contamination	Annually (minimum)	$25 - $50
E. coli	Confirms fecal contamination specifically	Annually (minimum)	$25 - $50
Nitrates	Wastewater-related nutrient contamination	Annually	$15 - $35
Full water panel (bacteria + chemicals)	Full baseline screening	Every 3-5 years or when buying a home	$100 - $300

Testing costs based on 2025-2026 pricing from TCEQ-accredited Texas laboratories.

Where to get your water tested:

• TCEQ maintains a list of accredited laboratories that test private well water
• Your county extension office (Texas A&M AgriLife Extension) may offer testing or referrals
• Some county health departments provide testing programs
• Private labs like National Testing Laboratories or local Texas labs offer mail-in kits

How to collect a proper sample:

• Use a sterile container provided by the lab (or a new, unused container)
• Collect the sample from a faucet closest to the well (before it passes through a water softener or filter)
• Run the water for 2 to 3 minutes before collecting
• Don't touch the inside of the container or cap
• Keep the sample cool and deliver to the lab within 24 hours (or per lab instructions)

What Do Coliform Bacteria Test Results Mean?

A positive coliform test doesn't always mean your well is contaminated by your septic system, but it does mean something is allowing bacteria into your water and you need to investigate.

Result	What It Means	Action
Total coliform: absent	Water is safe	Continue annual testing
Total coliform: present, E. coli: absent	Some bacterial contamination, not necessarily from sewage	Retest, inspect well cap and casing, disinfect well
Total coliform: present, E. coli: present	Fecal contamination confirmed	Stop drinking water immediately, disinfect well, inspect septic system
Nitrates above 10 mg/L (EPA safe drinking water standard)	Possible septic or agricultural contamination	Investigate source, don't give water to infants, treat or find alternative supply

Total coliform bacteria are found in soil, plants, and animal waste. Their presence means something is getting into your well that shouldn't be, but it's not necessarily sewage. Common causes include a cracked well cap, damaged casing, or surface water seeping in.

E. coli in your water is the clear warning sign. E. coli in a well water sample almost always indicates fecal contamination, and your septic system is the most likely source if it's within a few hundred feet.

What Should You Do If Your Well Water Tests Positive?

Stop using the water for drinking and cooking immediately. Retest to confirm, shock-chlorinate the well, and inspect both the well casing and septic system for the contamination source.

Follow these steps:

1. Stop drinking the water. Use bottled water or boil water for at least 1 minute before drinking or cooking. Continue until you get a clean retest.
2. Retest to confirm. A single positive result can sometimes be caused by improper sampling. Have the lab run a second test on a new sample.
3. If confirmed, shock-chlorinate the well. This involves adding a concentrated chlorine solution to the well to kill bacteria. Your well driller or a water treatment company can do this, or you can follow the Texas A&M AgriLife Extension guide for DIY shock chlorination.
4. Inspect the well. Have a well professional check the well cap, casing, and grout seal. These are the most common entry points for bacteria.
5. Inspect the septic system. Schedule a full septic inspection to check for leaks, drain field failure, or other problems that could be sending contamination toward your well.
6. Retest after disinfection. Wait 7 to 10 days after shock chlorination, then retest. If the water comes back clean, resume normal use with increased monitoring (test every 3 months for a year).
7. If contamination persists, consider installing a point-of-use water treatment system (UV disinfection or reverse osmosis) and consult with TCEQ or your county health department about long-term solutions.

How Do You Maintain a Well and Septic System Together?

Good maintenance of both your well and septic system is the best way to prevent contamination. Here's a dual-system maintenance schedule.

Task	Frequency	Why It Matters
Test well water (coliform + nitrates)	Annually	Catches contamination early
Pump septic tank	Every 3-5 years	Prevents solids from reaching drain field
Inspect well cap and casing	Annually (visual check)	Prevents surface contamination from entering well
Inspect septic system (full inspection)	Every 3-5 years	Identifies failing components before they contaminate groundwater
Inspect aerobic system	Every 4 months (TCEQ requirement)	Keeps treatment quality high
Check drain field	Seasonally (walk the area)	Catches soggy spots, odors, or surfacing early
Grade surface water away from well	As needed	Prevents runoff from carrying contaminants to well

Other best practices:

• Keep records of all well tests and septic service visits
• Don't use the area between your well and septic system for activities that could contaminate groundwater (no chemical storage, no fertilizer application, no vehicle parking)
• If you replace either system, use it as an opportunity to increase the separation distance if possible
• Make sure your well is uphill from your septic system if the terrain allows it (contaminants flow downhill through groundwater)

Well Water Treatment Options Compared

Treatment	Cost	What It Removes	Maintenance	Best For
UV disinfection	$200-$500	Bacteria, viruses	Lamp replacement every 12 months ($30-$60)	Homes near setback minimum
Reverse osmosis (point-of-use)	$200-$600	Bacteria, nitrates, chemicals	Filter replacement every 6-12 months ($50-$100)	Homes with nitrate concerns
Shock chlorination	$100-$200 per treatment	Bacteria (temporary)	As needed after contamination	Emergency decontamination
Whole-house UV	$500-$1,500	Bacteria, viruses (all taps)	Lamp replacement annually ($50-$100)	Homes with recurring contamination

UV disinfection is the most cost-effective ongoing protection for homes near the setback minimum. Reverse osmosis adds nitrate removal but treats only one tap. For persistent contamination, a whole-house UV system paired with point-of-use RO at the kitchen tap provides the most complete protection.

Which Texas Aquifers Are Most Vulnerable to Septic Contamination?

Texas has 9 major and 22 minor aquifers, and each has different vulnerability to septic contamination (Texas Water Development Board, 2024 State Water Plan).

Aquifer	Location	Vulnerability	Key Concern
Edwards (Balcones Fault Zone)	Central Texas, Hill Country	Very high	Karst geology allows rapid contamination transport
Trinity	North Central Texas, Hill Country	Moderate to high	Fractured limestone provides pathways
Ogallala	Texas Panhandle, West Texas	Moderate	Declining water levels increase concentration of contaminants
Gulf Coast	Houston, Coastal Bend	Moderate	Shallow wells at higher risk
Carrizo-Wilcox	East Texas, Winter Garden	Lower	Better natural filtration in sandy soils

Edwards Aquifer protections: The Edwards Aquifer is the most protected groundwater resource in Texas due to its karst geology and its role as the primary water supply for San Antonio and surrounding communities. Properties in the recharge zone face:

• Additional TCEQ permit requirements for septic systems
• Prohibition of certain system types (like seepage pits)
• Stricter setback distances in some areas
• Edwards Aquifer Authority (EAA) review and approval
• Requirements for aerobic systems with higher treatment levels in some zones
• Monitoring and reporting requirements beyond standard OSSF rules

If your property is in the Edwards Aquifer recharge or transition zone, work with your county and the EAA to understand the specific rules that apply.

What to Do Next

If you have both a well and a septic system:

1. Know your setback distances. Measure the distance between your well and your septic components. If they're closer than required, consider having an engineer evaluate your situation.
2. Start annual testing if you're not already doing it. A $50 water test is cheap insurance.
3. Stay on top of septic maintenance. Regular pumping and inspections protect your well water.
4. Keep records of all test results and service visits. These are valuable for your own tracking and for real estate transactions.

Need septic service or a system inspection? Find septic companies in your area

Frequently Asked Questions

How far should a well be from a septic tank in Texas?

TCEQ requires a minimum of 50 feet between a private water well and a septic tank or drain field. For public water supply wells, the drain field must be at least 150 feet away. Some counties require greater distances, especially in environmentally sensitive areas like the Edwards Aquifer recharge zone. If your well and septic are closer than these minimums and were installed before current rules, they may be grandfathered, but you should test your water more frequently.

Can a septic system contaminate my well if it's more than 50 feet away?

Yes, though the risk decreases with distance. In karst terrain (common in Central Texas), contaminants can travel hundreds of feet through underground fractures and channels. In clay soil, 50 feet usually provides adequate filtration. The 50-foot minimum is a general safety standard, not a guarantee. Annual water testing is the only way to know for certain that your well is safe.

How quickly can septic contamination show up in a well?

It depends on soil type and geology. In sandy or karst terrain, contamination can reach a nearby well within days to weeks. In clay soil, it may take months to years. After a septic failure or heavy flooding, test your well water right away and again 2 to 4 weeks later. Some contamination events are immediate, while others build gradually.

Should I treat my well water if I have a septic system?

Point-of-use treatment (UV light or reverse osmosis at the kitchen tap) is a good precaution, especially if your well is near the minimum setback distance or if you've had a positive test in the past. UV systems cost $200 to $500 and kill bacteria without chemicals. Reverse osmosis systems ($200 to $600) remove bacteria, nitrates, and many other contaminants. Neither replaces proper septic maintenance, but they add a safety layer.

What do I do if my neighbor's septic is too close to my well?

Contact your county's TCEQ-authorized agent to report the concern. If a neighboring property's septic system was installed in violation of setback requirements, the county can require the property owner to remediate the situation. If the system was installed before current rules took effect, the county may not be able to force changes, but you should increase your water testing frequency and consider adding point-of-use treatment to your well system.

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Last updated: February 2026 Reviewed by: Texas Septic Guide Editorial Team, TCEQ regulatory research Sources: TCEQ 30 TAC Chapter 285/290, Texas A&M Water Resources Institute, Texas A&M AgriLife Extension Service, Edwards Aquifer Authority