Do I need a perc test for a septic system?

NationwideReviewed October 2026

It depends on the state. A percolation (perc) test measures how fast water soaks into soil, and many states use perc rates or soil evaluations to size a drainfield; Virginia Cooperative Extension, for example, describes licensed evaluators measuring percolation rates. The Texas rule instead builds its site evaluation around soil excavations: at least two borings or pits, with soil texture classification, restrictive layers and groundwater recorded by a licensed site evaluator or engineer. Texas A&M AgriLife explains that soil texture sets how fast effluent moves and therefore how large the field must be, with sandy soils best and clay problematic. Ask your permitting office which test method it accepts.

Check your local rule. This varies by state, county or city. Your permitting office has the final word; the official lookup pages below show you who that is.

Sources

Find the rule for your area

Official pages from the agencies and code bodies that set these rules.

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General information, written in our own words from the sources listed with each answer. It is not legal, engineering, tax or financial advice. Rules change and differ by state, county and city, so confirm with the office that issues your permit before you build. Last reviewed October 2026.