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What is a Percolation Test?

Mary McMahon
Updated May 21, 2024
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A percolation test is a test which is performed during the course of a site evaluation. Percolation tests are conducted to find out whether or not a septic system can be installed on site, and to gather information which will be used to design the system. People are usually required to submit the results of a percolation test to public health authorities before they will be allowed to get a permit for a septic system, and a permit for a septic system is usually needed to obtain a building permit if a lot cannot be collected to municipal water and sewer. Therefore, percolation tests are critical during the evaluation stages of property development in many areas of the world.

Also known as a “perc test,” a percolation test is designed to see how well the soil can absorb water. This will play a direct role in determining whether or not the soil can support a septic system. The results may also indicate how large the system will be, where it can be installed, and how it should be designed. For example, the results of the test may indicate that a site is only suitable for a single family home, not a duplex or larger development, which can impact how the property will be developed.

To conduct a percolation test, a series of holes are dug, and the sides of the holes are roughened before the holes are presoaked. The presoak takes place the night before the percolation test. On the morning of the test, residue is removed from the holes, and a controlled amount of water is poured in. The reading of the test results is based on how long it takes the soil to absorb the water added to the hole.

This test is often monitored and administered by a health department official. The official confirms that the test was conducted properly, notes down the readings, and issues a formal report after the test is concluded.

Site evaluation includes a number of tests beyond percolation tests. In some cases, a real estate agent will sell a site which has already been evaluated, with test results indicating how the site can be used and providing important information about conditions at the site. A pre-evaluated site can be more appealing to buy, because people will not be going into the purchase without any knowledge of how the site can be used. If the evaluation also includes permits, it can be especially appealing to potential buyers.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By andee — On Sep 13, 2011

I never had any idea what a percolation test was until we had to have a septic system installed for our house.

I know my husband was quite anxious to get the percolation test results because there weren't very many options where we could dig the laterals for the septic system.

He was relieved when the results came back OK and he could go ahead with his original plan.

By golf07 — On Sep 12, 2011

Many years ago we bought several acres of land in the country. We didn't begin building our house for about 5 years after we bought the land.

Before we began building, we had to have a well dug and a soil percolation test done for the septic system.

I don't remember much about the process other than the results of the percolation test had to be verified before we had permission to continue.

We lived there for many years and never had any problems with either the well or the septic system.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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