Percolation Test – How to and Do I need to do one

What is a percolation test used for?

A percolation test is a requirement needed before you can install a new soakaway system or make changes to an existing soakaway. It helps you to determine the amount of time it takes for water to soak into your soil.

Do I need to do a percolation test?

If you are thinking of adding a soakaway system or replacing an old soakaway you will need to check the suitability of your ground beforehand. Some soil types are not suitable for soakaway systems.

Can I do my own percolation test?

Best to check with your local council, depending on your area and size of soakaway you may need a company registered with the council to perform the test for you. Otherwise, your good to go yourself.

Is a percolation test mandatory?

It is an important test if you want your soakaway to be successful. In some areas it is a requirement of adding a soakaway system.

What does a percolation test for?

A percolation test measures how long it takes an amount of water to drain from a set area. This will allow you to measure the suitability for drainage.

Please note If you want to install a septic tank or other dispersal systems you will additionally need to test for suitability.


How do I perform a percolation test?

  1. Dig 2 test holes within your proposed soakaway area.
  2. Dig the holes 300mm square
  3. Dig the holes below the planned level of the crate /outlet pipe 300mm
  4. Fill the hole with water to 300mm
  5. Time how long the water takes to drain. If the water does not drain, then your soil type is unsuitable for a soakaway system.
  6. When the water in the test hole is ¾ full, time how long it takes until the water has drained away to ¼ full.
  7. This time measurement will help you work out the Vp number.
  8. Repeat test at least 3 times and average your results for both test holes.
  9. First multiply your average time by 60
  10. Then divide your answer 150 (the amount the water has gone down) to give you the time it takes for the water to disperse.
  11. If your result is between 15-100 you have a perfect soakaway situation. Your ground will provide a slow and steady soakaway solution.

How are percolation test results calculated? – Vp


45 minutes to reduce from ¾ to ¼ in the test hole. (Average over at least 3 tests in 2 test sites)


2700/150 = 18

Vp – 18


Check out our soakaway kits in the drainage and soakaway section.



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