Many areas of South Africa are supplied with water borne sewage systems. But as urban areas become more and more built up, and many new developments have to be further out of main centers, the chances are good that any vacant land sold will have to be suitable for septic tank installation, and any developer wanting to buy that land for business or residential purposes will first need to conduct a percolation test.

No, we’re not talking about coffee, although the basic principle is the same. Any land without a municipal sewerage system has to pass a percolation test before any building permission will be given. It is therefore essential for this test to be carried out before you purchase the land.

What Is A Percolation Test?

Typically, a percolation test consists of at least three holes, which are dug approximately 10 to 12 meters apart in the proposed drainage area. Five centimeters of clean sand or gravel are placed in the bottom of each hole and the soil is then “pre-soaked” for several hours to mimic a working septic tank system as closely as possible. The holes are then filled with water to a depth of about 15cm above the sand or gravel, and the rate at which the water drops in 30 minutes is carefully measured.

As a general rule of thumb, soils that have a high gravel and sand content drain the best, while those with solid rock or high clay content are the worst. Before conducting an “official” percolation test, you can test the suitability of the soil yourself by simply taking a handful of damp subsoil (the soil a few centimeters underneath the topsoil) and rolling it into a thin worm shape. If it holds together, the soil is high in clay and may well fail a percolation test.

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