Land records · Parcel maps · October 5, 2026
What Is a Perc Test? Septic Soil Testing Explained
What is a perc test? A soil test measuring how fast water drains to see if land can support a septic system. Process, cost factors, and failing results.
What is a perc test? A percolation test, or perc test, measures how quickly water soaks into the soil at a specific spot. Health departments use the results, often along with a soil evaluation, to decide whether a lot can support a conventional septic system and how large the drain field must be. On rural land without public sewer, a passing perc test can determine whether a lot is buildable at all. This page is general land-records background, not engineering or legal advice.
How a perc test works
- Holes are dug in the proposed drain field area, often several holes to a set depth.
- Holes are pre-soaked so soil is saturated, often overnight in traditional methods.
- Water is added and the drop in water level is timed.
- The rate is recorded, often in minutes per inch.
- A soil evaluation may also examine soil layers, color, and seasonal water table in a test pit.
Many jurisdictions now rely heavily on soil profile evaluations, with or without the traditional timed perc.
Reading results
| Result | Meaning |
|---|---|
| Too fast | Water drains too quickly to treat wastewater, as in coarse sand or gravel |
| Acceptable range | Suitable for a conventional system |
| Too slow | Clay or compacted soils that may not absorb effluent |
| High water table or rock | May limit or prevent conventional systems |
Acceptable ranges and methods are set by state and local health codes.
Who performs it
Licensed soil scientists, engineers, septic designers, or health department staff, depending on the state. The health department typically reviews results and issues a permit for the septic design.
Cost and timing
Costs vary by location, the number of holes, excavator time, and whether a soil scientist or engineer is required. Some areas limit testing to certain seasons to capture wet-season conditions.
If the lot fails
- Test another location on the lot.
- Consider alternative systems, such as mound systems, sand filters, drip irrigation, or aerobic treatment units, where allowed. These often cost more.
- Connect to public sewer if available.
- Reconsider the purchase if no option works.
Buying rural land
Make a purchase contract contingent on a passing perc test or septic permit. Check whether an old perc result is still valid; some expire or depend on lot changes. Also confirm the septic reserve area requirements, which may require space for a replacement field.
Where perc results show up in records
Perc and soil evaluation results are usually kept by the county or district health department, not the recorder. Some subdivision plats include notes about approved septic areas or lots that require special systems, and some counties link septic permits to the parcel in an online viewer. Ask the health department for any file on the parcel before you buy.
Bottom line
A perc test measures how fast soil absorbs water to determine whether a lot can support a septic system and how big it must be. Results and methods follow local health codes, and failing lots may need alternative systems. Make rural land purchases contingent on septic approval. Check parcel details on the Platbookmapper map.
What is a perc test FAQ
What does a perc test tell you?
How quickly soil absorbs water, which helps determine whether a septic system will work.
Who does a perc test?
Licensed soil scientists, engineers, designers, or health department staff, depending on the state.
What happens if land fails a perc test?
You may test another spot, use an alternative septic system, connect to sewer, or reconsider building.
Do perc tests expire?
Some do, or may need updating if lot conditions or rules change. Check with the health department.
Should I buy land without a perc test?
It is risky. Many buyers make purchases contingent on a passing test or septic permit.