What Is a Perc Test in Texas? (Cost, Process, and Requirements)

A perc test measures how fast soil absorbs water. In Texas, it costs $250-$600, is required before any septic install, and takes 1-3 days.

If you're building a new home on rural land, buying property without city sewer, or replacing a septic system, you'll almost certainly need a perc test. According to the EPA, roughly 1 in 5 U.S. homes rely on septic systems, and Texas alone has over 2.6 million. A perc test tells you whether your soil can handle a standard septic system or if you'll need an alternative design.

Key Fact	Details
What it measures	How fast soil absorbs water (minutes per inch)
Cost	$250 to $600 (most homeowners)
How long it takes	3 to 7 days total, 1-2 days of field work
Who performs it	TCEQ-licensed site evaluator
Required for	New septic install, replacement, or major modification
Pass rate range	5-60 MPI for conventional systems
If you fail	Alternative systems available ($8,000-$30,000)

The EPA considers soil evaluation one of the most critical steps in septic system siting, since the soil itself provides the final stage of wastewater treatment. This guide covers how perc tests work in Texas, what they cost, and what to do if your land fails one.

How Does a Perc Test Work?

An evaluator fills test holes with water, then measures how fast it drops. The result, in "minutes per inch" (MPI), determines your septic options.

Here's the basic process:

1. A licensed site evaluator digs several test holes (usually 6 to 12 inches deep) in the area where your drain field would go.
2. The holes are filled with water and left to soak for 4 to 24 hours. This presoak step simulates what happens when the soil is already wet from rain or regular use.
3. After presoaking, the evaluator refills the holes and measures how fast the water level drops, checking every 15 to 30 minutes.
4. The slowest hole determines your overall result. If one hole drains at 45 MPI and another at 20 MPI, your site is rated at 45 MPI.
5. The evaluator writes up a report documenting soil conditions, drainage rates, and any concerns like high water table or rock layers.

What the numbers mean:

Perc Rate (MPI)	Soil Drainage	What It Means for Your Septic
Less than 5	Too fast	Water drains before treatment. May need enhanced system.
5 to 30	Good	Standard conventional septic system will work.
30 to 60	Moderate	Conventional may work with larger drain field.
60 to 120	Slow	Likely need aerobic system or alternative design.
Over 120	Very slow	Standard septic won't work. Need mound, drip, or other alternative.

Most of Central Texas sits on clay soil that tends toward slower drainage. Hill Country properties often hit limestone rock. Both situations are common, and both have solutions. As Texas A&M AgriLife Extension notes, "to function properly, a septic system must be surrounded by good-quality, non-compacted soil," which is exactly what a perc test verifies.

When Do You Need a Perc Test in Texas?

Texas requires a perc test (technically called a "site evaluation") before you can get a permit to install, replace, or significantly modify any septic system.

You'll need one if you're:

• Building a new home on land without city sewer access
• Replacing an existing septic system that has failed
• Buying raw land and want to confirm it can support a septic system before closing
• Adding onto a home in a way that increases bedrooms or wastewater load
• Subdividing property where each lot needs its own septic

TCEQ (Texas Commission on Environmental Quality) oversees the rules statewide through 30 TAC Chapter 285, which requires a site evaluation for all on-site sewage facility permits. Your county's designated representative (usually the county health department or an environmental services office) handles the actual permitting.

One exception: Texas has a limited 10-acre exemption. If your property is 10 acres or more, used only as a single-family home, and the septic system is at least 100 feet from property lines, you may not need a permit. But even exempt properties benefit from a site evaluation to avoid expensive surprises during construction.

How Much Does a Perc Test Cost in Texas?

Most Texas homeowners pay $250 to $600 for a perc test, depending on the property's size, location, and how many test holes are needed.

Factor	Cost Impact
Standard perc test (3-6 holes)	$250 - $450
Complex site (rocky soil, slopes, extra holes)	$400 - $600
Full site evaluation (perc + soil profile + report)	$400 - $800
Expedited results	+$50 - $150

A few things that affect your price:

• Number of test holes. More holes means more labor. Some counties require a minimum of 3 holes, while others want 6 or more.
• Soil conditions. Rocky or extremely hard soil takes longer to dig and may require special equipment.
• Property access. Remote properties or sites without cleared paths can add to the cost.
• County requirements. Some counties require the evaluator to be present for the full presoak period (24+ hours), which increases the fee.

The perc test is usually part of a larger site evaluation that your septic designer or installer coordinates. Per TCEQ's on-site sewage facility (OSSF) program rules, the site evaluation must be conducted by a licensed professional and documented in a formal report. Many Texas septic companies bundle the perc test with system design for a package price.

What's the Perc Test Process Step by Step?

From scheduling to getting your results, a perc test in Texas typically takes 3 to 7 days, with the actual field work happening over 1 to 2 days.

Here's what to expect:

Before the test:

• Hire a licensed site evaluator (your county can provide a list, or ask your builder)
• Clear the proposed drain field area of brush and debris
• Mark any existing wells, property lines, or buried utilities
• Check if your county requires you to pull a permit just for the evaluation itself

Day 1: Digging and presoaking

• The evaluator digs test holes at the proposed drain field location
• Holes are filled with water for the presoak period (4 to 24 hours depending on soil type and county rules)
• Some evaluators also dig a soil profile pit to examine soil layers, texture, and any restricting layers like rock or hardpan

Day 2: Measuring drainage

• The evaluator returns, cleans loose soil from the holes, and refills them to a set level
• Water drop is measured at regular intervals (typically every 15 to 30 minutes)
• Measurements continue until a consistent rate is achieved (usually 3 to 6 readings)

After the test:

• The evaluator prepares a written report with drainage rates, soil observations, and recommendations
• The report goes to your county permitting office as part of your septic permit application
• Results are typically available within 1 to 3 business days after field work

What Happens If Your Perc Test Fails?

A failed perc test doesn't necessarily mean you can't build. It means you'll need an alternative septic system designed for your soil conditions, which costs more but is usually possible.

Your soil might "fail" for several reasons:

• Too slow (high MPI): Heavy clay soil that doesn't drain fast enough for a conventional system
• Too fast (low MPI): Sandy or gravelly soil that drains so quickly, wastewater doesn't get properly treated
• High water table: Groundwater sits too close to the surface for a standard drain field
• Shallow rock: Limestone or other rock layers prevent adequate soil treatment

Alternative systems for failed perc tests in Texas:

System Type	Best For	Approximate Cost
Aerobic treatment unit	Slow-draining soil, small lots	$10,000 - $20,000
Mound system	High water table, shallow rock	$12,000 - $25,000
Low-pressure pipe (LPP)	Moderate drainage issues	$8,000 - $15,000
Drip irrigation system	Poor soil, tight lots, slopes	$15,000 - $30,000
Evapotranspiration system	Arid areas with low rainfall	$10,000 - $20,000

Aerobic systems are the most common alternative in Texas. They use air to speed up the treatment process, producing cleaner wastewater that's safer for challenging soil conditions. Per TCEQ regulations (30 TAC Chapter 285, Subchapter D), all aerobic systems require a two-year maintenance contract with a licensed provider. For a deeper comparison, see our guide on aerobic vs. conventional septic systems in Texas.

Conventional vs. alternative: what's the real cost difference? A conventional septic system typically costs $3,000-$8,000 to install. If your perc test requires an alternative system, expect $8,000-$30,000 depending on the type. That's a significant jump, but it's still far less than the cost of buying land you can't build on at all.

Can you retest? Yes. If conditions change (for example, you test during an unusually wet season and the water table was high), you may be able to retest. Talk to your evaluator about timing. Some counties allow retesting in a different area of the property.

County-by-County Differences in Texas

Perc test requirements vary by county in Texas because each county acts as TCEQ's local authorized agent and can add stricter rules on top of statewide standards.

Here are some examples of how counties differ:

County	Notable Requirements
Travis County	Stricter setback requirements, extra review for environmentally sensitive areas near Edwards Aquifer
Harris County	Online E-Permits system, additional documentation for properties near wells
Williamson County	Requires soil report with application, specific form requirements
Hays County	Edwards Aquifer protection rules apply in portions of the county
Kendall County	10-14 working day review period, requires 3 copies of plans and original soil report
Bexar County	Additional requirements in Edwards Aquifer recharge zone

What this means for you: Always check with your specific county before scheduling a perc test. The evaluator should know your county's rules, but it's worth confirming:

• How many test holes are required
• Whether a county inspector needs to witness the test
• What forms and documentation the county expects
• Whether there are seasonal testing restrictions
• What additional setback or environmental rules apply to your property

Your county's TCEQ-authorized representative is usually the health department or environmental services office. Per TCEQ's authorized agent program, each county maintains its own permitting procedures within the statewide framework of 30 TAC Chapter 285. TCEQ maintains a full list of authorized agents on their website.

Tips for a Successful Perc Test

The single best move is testing before you buy the land, so you can make the sale contingent on passing results and avoid costly surprises.

• Test before you buy land. If you're purchasing rural property for a new build, make the sale contingent on a passing perc test. This protects you from buying land you can't build on.
• Test in typical conditions. Avoid testing during extremely wet or dry periods if possible. Unusual conditions can skew results.
• Hire a licensed evaluator. Texas requires a TCEQ-licensed site evaluator. Don't try to do this yourself, even if your property qualifies for the 10-acre exemption.
• Plan for alternatives. If your property has clay soil or you're in the Hill Country, budget for the possibility of needing an aerobic or alternative system.
• Keep your report. Your perc test results are valuable documents. Keep copies for your records, your builder, and future reference if you ever sell the property.

Need a perc test in Texas? Find licensed septic professionals in your area

Frequently Asked Questions

How long is a perc test valid in Texas?

Most Texas counties accept perc test results for 1 to 2 years, though some may require a new test if conditions have changed significantly. If you get a perc test done and don't start construction for a while, check with your county to see if you need a fresh evaluation. Major changes like nearby construction, flooding, or drought can affect soil conditions.

Can I do a perc test myself in Texas?

No, Texas requires a licensed site evaluator to perform the test for permit purposes. While you can dig a hole and pour water in to get a rough idea of your soil's drainage, only a TCEQ-licensed professional's report will be accepted for your septic permit application. The evaluator's credentials are part of the official record.

What's the difference between a perc test and a soil test?

A perc test measures drainage speed (how fast water moves through soil), while a soil test examines the actual composition, layers, and texture of the soil. Both are typically done as part of a complete site evaluation. The soil profile test involves digging a deeper pit to look at soil layers, check for rock, and identify the water table. Together, they give a full picture of whether your site can support a septic system.

Does a failed perc test lower my property value?

It can, but it doesn't make land worthless. Properties that can't support conventional septic systems are still buildable in most cases using alternative systems. The main impact is higher construction costs for the septic system itself. Be upfront with potential buyers about soil conditions and what alternative systems are available. Many Texas properties, especially in the Hill Country and Blackland Prairie, need alternative systems due to clay soil or limestone.

When is the best time of year to do a perc test in Texas?

Spring and fall typically provide the most representative results in Texas. Summer drought can make soil appear to drain faster than it normally would, while testing right after heavy rains can make drainage appear slower. Your evaluator can help you time the test for the most accurate results based on your county's soil conditions.

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Last updated: February 7, 2026 Reviewed by: Texas Septic Guide Editorial Team, TCEQ regulatory research