Williamson County Septic Regulations: What Homeowners Need to Know in 2026

Williamson County septic permits cost $510-$710 for residential systems, are issued by the County Engineer's Office, and require two-year aerobic license renewals.

Williamson County sits just north of Austin and includes fast-growing cities like Round Rock, Cedar Park, Georgetown, and Leander. According to TCEQ data, roughly 45,000 new on-site wastewater treatment systems are installed across Texas each year, and Williamson County's rapid growth means a significant share of those go in right here. The county's 2021 Order Adopting Rules for On-Site Sewage Facilities sets requirements that go beyond base TCEQ standards in several areas.

If you live in unincorporated Williamson County or in a city's extraterritorial jurisdiction (ETJ), your septic system falls under the county's rules. This guide covers permits, fees, the application process, aerobic requirements, and enforcement specific to Williamson County.

Who Handles Septic Permits in Williamson County?

The Williamson County Engineer's Office runs the On-Site Sewage Facility program, issuing all septic permits for unincorporated areas and ETJs.

Per TCEQ's authorized agent program, Williamson County administers the state's septic program locally under 30 TAC Chapter 285, Texas Health and Safety Code Chapter 366, and Texas Water Code Chapters 7 and 37. The county has adopted its own order with stricter rules in several areas.

Before applying, check whether your property falls under county jurisdiction. Use the County Address Search tool on the Williamson County website. If the result shows "Unincorporated" or lists an ETJ, the county handles your septic permits. Properties within the City of Austin (even those geographically in Williamson County) go through Austin's permitting process instead.

Contact information:

Detail	Information
Office	Williamson County Engineer's Office, Septic Permit Program
Phone	(512) 943-3330
Email	ossf@wilcotx.gov
Online portal	wilcotx.gov/644 (Septic Permits)
Application system	MyGovernmentOnline
Fee calculator	wilcotx.gov/422

All applications go through the MyGovernmentOnline platform. Paper and email applications are not accepted. The county provides a Permit Fee Calculator on their website so you can estimate costs before you start.

What Are the Septic Permit Types and Fees in Williamson County?

Williamson County publishes a clear fee schedule updated September 2025. Residential conventional permits cost $510, non-conventional $610, and aerobic systems $710.

Here's the full fee schedule:

Permit Type	Fee	Notes
Residential conventional	$510	Standard anaerobic systems
Residential non-conventional (non-aerobic)	$610	Mound, low-pressure dose, etc.
Residential aerobic treatment unit	$710	Includes spray or drip systems
Commercial non-aerobic	$810	Business and institutional
Commercial aerobic	$910	Business with aerobic treatment
Extra site visit / reinspection	$100	Per additional visit
New/additional design review	$150	Added to base permit fee
Aerobic license renewal/transfer	$60	Required every two years
TCEQ state fee	$10	Added to all permits

These are among the most transparent and detailed fee schedules of any Texas county. Use the county's online Permit Fee Calculator to estimate your total before applying.

The 10-acre exemption: Williamson County's local rules don't explicitly reference the standard TCEQ 10-acre exemption in available documentation. Under base TCEQ rules (30 TAC Chapter 285), properties of 10 acres or larger with a single home and proper setbacks may qualify. But given the county's strict local order, contact the Engineer's Office at (512) 943-3330 to confirm before assuming you're exempt.

How Does the Williamson County Septic Permit Process Work?

The permit process runs entirely online through MyGovernmentOnline, with inspections at key construction phases and a License to Operate issued after final approval.

Here's the step-by-step process:

1. Check your jurisdiction. Use the County Address Search tool to confirm Williamson County handles your property's septic permits. ETJ properties fall under county jurisdiction.

2. Site evaluation. Hire a Professional Engineer (PE) or Licensed Professional Sanitarian to evaluate your soil, run percolation tests, and design the system. Complete the county's Soil Evaluation Form and Site Evaluation Checklist.

3. Gather documents. You'll need: warranty deed, property survey, site plan with system design, soil evaluation report, and the appropriate checklists. Properties in the Edwards Aquifer Recharge Zone need to reference the Williamson County EARZ Map for septic systems. For aerobic systems, include a maintenance contract or notarized Routine Maintenance Affidavit.

4. Submit application online. Log into MyGovernmentOnline, upload all documents, and pay fees. No paper or email submissions accepted.

5. County review. The Engineer's Office reviews your application against the 2021 County Order and 30 TAC Chapter 285. Review times vary by workload and complexity.

6. Authorization to construct. Once approved, you receive authorization to begin installation. Only a TCEQ-licensed installer can do the work.

7. Inspections. County inspectors check the installation at critical phases. No components can be covered until approved. Extra site visits cost $100 each.

8. License to Operate. After the system passes final inspection, you receive your License to Operate. For aerobic systems, this license must be renewed every two years.

How Do Williamson County Septic Rules Differ from TCEQ Minimums?

Williamson County's 2021 Order adds requirements for pump tank reserve capacity, capped risers on all tanks, and no variances for lot sizing or density.

These are the key differences from base TCEQ standards:

No variances for lot sizing or density. Other counties sometimes grant variances for undersized lots. Williamson County does not. If your lot doesn't meet the sizing requirements for your proposed system, you need a different system design, not a waiver.

Pump tank reserve capacity. All pump tanks must include reserve capacity beyond the minimum required volume. This gives the system a buffer if the pump fails or if water usage spikes.

Capped risers and cleanouts. Every septic tank must have capped risers and cleanouts that reach ground level for monitoring. This makes inspections and maintenance easier and is a practical improvement over the base TCEQ standard.

Subdivision compliance required. Tracts that were subdivided without following Williamson County Subdivision regulations can't get septic permits. This catches properties that were informally divided without proper platting.

Two-year permit validity. Permits are valid for two years initially. Aerobic systems must be renewed every two years with a current maintenance contract or affidavit and an inspection report.

Setback requirements:

Feature	Minimum Distance
Property line	5 feet
Water well (tank)	50 feet
Sewer pipe	50 feet
Fields (except drip and lined ET)	150 feet

Properties in the Edwards Aquifer Recharge Zone (parts of western Williamson County) may need a TCEQ Water Pollution Abatement Plan. Check the Williamson County EARZ Map available on the county website.

What Are the Aerobic System Requirements in Williamson County?

Aerobic systems in Williamson County require a TCEQ-registered, county-approved maintenance provider and a two-year license renewal with inspection report.

Here's what Williamson County expects for aerobic treatment units:

Maintenance provider requirements. Your aerobic system must be maintained by a provider who is both TCEQ-registered and approved by Williamson County. Homeowners generally can't self-maintain unless they've been authorized as maintenance providers and filed a notarized Routine Maintenance Affidavit with County Records.

Two-year license renewal. Your License to Operate for an aerobic system must be renewed every two years. The renewal requires a current maintenance contract (or affidavit if self-maintaining), an inspection report, and a $60 renewal fee. Miss this renewal and your license lapses.

Self-maintenance option. If you want to maintain your own aerobic system, you need to submit a notarized Routine Maintenance Affidavit filed in County Records and upload it via MyGovernmentOnline as part of your application. Failing to complete this process voids the self-maintenance authorization.

What the maintenance provider checks:

• Aerator and blower operation
• Alarm system function
• Disinfection unit condition
• Spray heads or drip emitters
• Treated water quality
• Overall system performance

Budget $500-$700 every two years for a standard aerobic maintenance contract in the Round Rock/Georgetown area. The $60 license renewal fee is on top of that.

What Happens If You Violate Williamson County Septic Rules?

Williamson County investigates complaints about exposed sewage and can issue legal notices of violation with potential court action.

The enforcement process follows the standard Texas framework:

What triggers enforcement:

• Operating without a permit
• Installing or modifying a system without authorization
• Failing to maintain or renew an aerobic system license
• Exposed sewage or system causing a nuisance
• Systems on improperly subdivided tracts
• Failing required inspections

Complaint process: Contact the Engineer's Office at (512) 943-3330 or email ossf@wilcotx.gov. The county investigates complaints about exposed sewage and non-compliant systems.

Enforcement actions: Williamson County can issue notices of violation and pursue court action for non-compliance. According to Texas Health and Safety Code Chapter 366, willful septic violations are Class C misdemeanors carrying fines up to $500 per day. TCEQ can also pursue civil penalties for serious violations.

Unpermitted work: All installation, repair, and modification work requires a permit and a TCEQ-licensed installer. The county's subdivision compliance rule means that even if your system design meets all technical standards, you can't get a permit if the underlying tract wasn't properly subdivided.

How Much Does Septic Work Cost in Williamson County?

A conventional septic system in the Round Rock/Georgetown area runs $6,300-$9,900 installed, while aerobic systems cost $7,800-$12,000. Williamson County permit fees add $510-$710.

Here's what homeowners in the area should budget:

Item	Cost Range
Conventional system install (3-bedroom)	$6,300-$9,900
Aerobic spray system	$7,800-$9,800
Aerobic drip system	$9,800-$12,000
Site evaluation and soil testing	$600-$1,200
County permit fee (residential)	$510-$710
Septic pumping (1,000-gallon tank)	$235-$280
Aerobic maintenance contract (2 years)	$500-$700
Aerobic license renewal (every 2 years)	$60
Typical repair (per hour + materials)	$275-$375/hour
Drain field replacement	$5,000-$12,000

Williamson County's permit fees are mid-range for the Austin metro area. The bigger cost driver is your system type. Properties with poor soil conditions or in the Edwards Aquifer Recharge Zone will need aerobic or engineered systems, pushing costs $2,000-$5,000 higher than conventional.

For a full breakdown of Texas septic costs, see our septic pumping cost guide.

Frequently Asked Questions

Do I need a permit for septic work in Williamson County?

Yes, all new installations, repairs, and modifications require a permit through MyGovernmentOnline. If your property is in unincorporated Williamson County or in a city's ETJ, the county handles your septic permits. Use the County Address Search tool to confirm jurisdiction. Routine pumping does not require a permit.

How much does a septic permit cost in Williamson County?

Residential permits cost $510-$710 depending on system type. Conventional systems are $510, non-conventional non-aerobic systems are $610, and aerobic systems are $710. Add $600-$1,200 for the required site evaluation. Extra inspections cost $100 each, and additional design review adds $150.

Who inspects septic systems in Williamson County?

The Williamson County Engineer's Office handles all septic inspections. Inspectors check the system at critical construction phases, and nothing can be covered until they approve it. Extra site visits cost $100. For aerobic systems, your maintenance provider handles ongoing service, but the county requires an inspection report with each two-year license renewal.

Can I do my own septic work in Williamson County?

Installation and repairs must be done by a TCEQ-licensed installer. For conventional systems, homeowners can handle basic maintenance. For aerobic systems, self-maintenance is possible but requires filing a notarized Routine Maintenance Affidavit with County Records and uploading it through MyGovernmentOnline. If you don't complete this process, the self-maintenance authorization is void.

Do ETJ properties need Williamson County septic permits?

Yes, ETJ properties within Williamson County fall under the county's septic permitting program. Use the County Address Search tool on the Williamson County website to check. If the result shows "Unincorporated" or lists an ETJ, the county handles your permit. The one exception: properties in the City of Austin's jurisdiction go through Austin's permitting process even if geographically located in Williamson County.

Are TCEQ septic rules changing in 2026?

TCEQ is working on a staff-initiated rulemaking project for OSSF regulations, estimated for completion by Spring 2026. The changes aim to improve clarity and consistency of the rules and reflect current practices. Until new rules take effect, Williamson County continues to enforce its 2021 Order alongside 30 TAC Chapter 285. Check the TCEQ website for updates.

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Last updated: February 8, 2026 Reviewed by: Texas Septic Guide Editorial Team, content verified against TCEQ regulations, Williamson County Order Adopting Rules for On-Site Sewage Facilities (2021), and 30 TAC Chapter 285

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Sources: Williamson County Engineer's Office, On-Site Sewage Facility Program; Williamson County Order Adopting Rules for On-Site Sewage Facilities (2021); Texas Commission on Environmental Quality (TCEQ), 30 TAC Chapter 285; Texas Health and Safety Code Chapter 366; Williamson County Septic Permit Fee Schedule (September 2025).

Serving Williamson County communities: Round Rock | Cedar Park | Georgetown