Updated June 15, 2026
Short answer
A percolation (perc) test measures how fast water drains through your soil. It's the single biggest factor in sizing your drainfield and choosing your system type — no septic system can be designed or permitted without it.
What it measures
The test gauges your soil's texture, class, and how quickly it absorbs water across the proposed drainfield area — the soil's loading rate.
Why it sets your system
Better-draining soil needs a smaller drainfield and may allow a conventional system; tighter, clay-heavy soil needs a larger field or an aerobic system. The result drives the whole design and cost.
What to expect
We perform the test, document the results, and design a permitted system around your actual site conditions — so it passes county inspection and performs for decades.
| Soil class | Typical texture | Loading rate (gal/ft²/day) | Drainfield, 3-bed home |
|---|---|---|---|
| Ib | Sandy loam, loamy sand | 0.38 | ~630 sq ft |
| II | Loam, sandy clay loam | 0.25 | ~960 sq ft |
| III | Clay loam, silty clay loam | 0.20 | ~1,200 sq ft |
| IV | Clay, silty clay | 0.10 | ~2,400 sq ft |
Quick Flow Septic installs new septic systems across Harris County · Montgomery County · Fort Bend County · Waller County · Liberty County.
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