What is a Percolation Test?
A percolation test (or perc test) is done to determine the absorption capacity of soil. This test is important for the design of a septic system and is therefore required in just about every civilized municipality in the world. This test is typically carried out while purchasing land, to understand the behavior of soil under moisture conditions.​

A perc test is conducted by drilling or digging a hole in the ground, pouring water into the hole and then observing the rate at which the water is absorbed into the soil. In most cases, a perc test will pass if the soils have a higher concentration of sand (because sand tends to absorb water at a much faster rate than clay or silt) and/or when the property is situated in an area with a low water table.

​​In most jurisdictions, a perc test is performed when an official from the county health department meets with the owner of the property and/or a licensed excavator to dig a hole and test the drainage rate of the soil on-site (they literally pour water in a hole and time how long it takes to drain through).

The Health Department determines and enforces the rules that govern when a property is suitable for a septic system, so it's critical that they be present to perform and/or observe the test in real-time.
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Depending on the Health Department's requirements, the location of the property, the building plans and the makeup of the soil – a perc test can be very simple and inexpensive, or it can be somewhat complicated and costly.