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What is a "perc" test and why do I need to know about it?

Updated: Sep 13, 2022

What the heck is a "perc" test anyway? A percolation test or soil suitability test are terms that mean the same thing.

You need to know if the lot or property you are investigating is not served by a public sewer system. This "perc" test is performed to make sure a septic system can be installed and function properly without contaminating the drinking water supply. This is typical in rural areas.

The results from these tests help determine the soil’s ability to accept effluent (wastewater) over a period of time.

These results also help determine what type of septic system is needed to meet the client’s needs, based on the soils, for government approval for a system to be installed.

NOTE: If the property will not perc, then no house can be built. However, there may be alternative systems available that can work. You will need to check with the local government to see what is acceptable.

How is this “perc” testing done?

This test is often accomplished by hiring a licensed soil scientist, a geotechnical engineer firm, or using the county environmental department. These professionals have several ways to perform the test but all are done by digging holes and testing the soils. The holes can be anywhere from a few inches wide and a few feet deep to several feet wide and several feet deep. The professionals will determine the type of testing needed based on the client’s desires.

NOTE: Make sure you allow enough time for these tests to be completed when writing up a contract. It may take several weeks or even a few of months to get the "perc" test results back. You would not want to close on a vacant lot or land until you get acceptable results back from the test. That is, if you want to build a house or structure that requires a septic system on that property.

Also, if a previous perc test was completed, confirm the permit and time on the permit, they do have an expiration date.

Now that you know the importance of a perc test when purchasing a lot or piece of land, make sure you do your homework prior to a contract closing. I hope that this will give you a better insight of why you need to know what a perc test is and what it does for you and your clients.

Need more information?

Check out this article Perc Testing and Soil Testing by Steve Bliss at

Here is a great video on Septic Systems by Seth Williams who is the host of RETipster on YouTube which focuses on providing real-world guidance for real estate investors.

Want to learn more about this topic? Check out “10 Things You Need To Know About Land.” An excellent resource to add to your real estate, home, or office library... or just carry as a pocket guide!


Cheryl L. Sain has been in the real estate industry for over 20 years and has executed thousands of land transactions with investors, developers, national builders, and individuals.


This information is provided as-is and does not in any way make or imply any guarantees as to an outcome. You will need to evaluate the information herein and consult appropriate professionals such as surveyors, attorneys, tax accountants, or any other professional agencies or broker-in-charge to acquire the information and guidance you need to help you make the decision that is best for you.


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