Before You Build: DIY Perc Test Guide

By LandCentral


Perc tests, or percolation tests, aren’t the most glamorous part of buying a property. Most people don’t even give them a second thought until it’s time to put in the septic tank. Yet making sure your future property is septic ready is the only way to ensure you don’t find yourself knee deep in the wrong kind of soil. Many perc tests are performed by county approved engineers before a property is put up for sale. However, if you’re anxious to find out if the little plot of land you’ve been eyeing is prime septic real estate, follow LandCentral’s DIY Perc Test Guide:


  • Shovel
  • Wooden stake (5 ft. long with 6 in. intervals painted lengthwise like a ruler)
  • timer
  • water

Step 1: Dig a hole

First, determine where you would like to place your septic tank. Make sure you choose an area where the ground slopes less than 30 percent to comply with septic system installation requirements. Then get to digging. Using a shovel, dig a hole roughly 3 – 5 feet deep.

Step 2: Fill the hole with water

Using a hose or watering can, fill the hole with water until the dirt surrounding the soil is completely saturated. Keep soaking the soil for several hours on and off so the water can absorb into the soil (clay soil should soak for at least 12 hours to fully saturate). Once you’re confident the soil is drenched, stick the wooden stake inside the hole and refill the hole with water. Write down your start number based on where the water line measures on the stake.

Step 3: Time it

Set your timer for 30 minutes. Once the timer goes off, measure the depth of the remaining water left in the hole on the stake. Write down the end number next to the start number.

Step 4: Calculate it

It’s time for some math. Calculate the percolation rate using this basic formula:

Initial water depth – final water depth = answer.

Then, 30 minutes divided by above answer.


Initial water depth = 20 inches.

Final water depth = 16 inches.

20 – 16 = 4 inches.

30/4 = 7.2

This means the perc rate is 7.2 minutes per inch.

Step 5: Compare the results

Compare your results with the local building codes in your area. Each county holds different requirements such as size of the septic tank, size of the house, and number of leach lines. Generally, a perc rate ranging between 15 – 105 minutes per inch is ideal. Anything above or below is considered unacceptable and could mean you need an alternative septic system or may not be able to build at all.

Once you’ve determined the soil’s ability to absorb fluids, you’ll still need a professional to test and sign off on the septic permit. Contact the environmental health department in the area. Some properties already come with a completed perc test, septic and a well. If they don’t, find out why and if it’s possible to put them in or make it contingent before you make your purchase. Doing this and other research on your property is good practice for any investment.

Remember, no perc = no house. Doing this simple DIY perc test can save you time and stress before you build.





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