Before spending money on a dry well, a rain garden, or a French drain, it helps to know one number: how fast your soil actually takes water in. A hole, a bucket, and an hour will tell you.
Why infiltration rate matters
Drainage solutions fall into two families. Some move water somewhere else — pipes, swales, channels. Others store water and let it soak in — dry wells, infiltration trenches, rain gardens.
The second family only works if the soil beneath will accept water at a reasonable rate. In the Piedmont, heavy clay frequently will not, which is why dry wells sometimes fail here.
Testing first is the difference between a solution and an expensive hole that stays full.
Running a simple test
This is not a formal engineered test, but it gives a useful picture of what your soil does.
- Dig a hole roughly twelve inches deep and eight to twelve inches across in the problem area.
- Scratch the sides so smearing from the shovel does not seal the hole.
- Fill it with water and let it drain completely to pre-soak the surrounding soil.
- Refill it and mark the starting water level.
- Measure the drop after one hour, and again if it is still holding water.
- Repeat in a second location — soil varies within a single yard.
Reading the results
Water gone within an hour or two means the soil drains well and infiltration-based solutions are on the table.
A drop of an inch or two per hour is moderate. Infiltration can work but needs generous sizing and realistic expectations during wet stretches.
Water still standing after several hours, or overnight, means infiltration is not the answer for that spot. The solution needs to convey water to an outlet instead of trying to soak it in.
Test after a wet period as well as a dry one if you can. Clay that takes water when dry can refuse it entirely when already saturated.
What the results change
Poor infiltration pushes the design toward collection and conveyance: catch basins, solid pipe, and a daylight outlet that is genuinely lower than the problem area.
Good infiltration opens up options that are often less disruptive — a dry well tucked out of sight, an infiltration trench, or a rain garden that doubles as a planting bed.
It also affects hardscape choices. Permeable paving depends on what is underneath it, which is why our article on permeable pavers in clay soil treats the base as the deciding factor.
Where this fits in a real project
For a small, isolated wet spot, a homeowner test is usually enough to pick a direction.
For anything involving the foundation, a slope, multiple problem areas, or a septic system, the test is one input among several — outlet elevation, drainage area, and existing site features matter just as much.
Southern Style Turf & Design assesses soil, grade, and outlet options together on drainage projects around Lake Norman so the design matches what the site can actually do.
Frequently asked questions
Is a homeowner percolation test the same as a septic perc test?
No. Septic evaluation is a regulated process performed by the health department or a licensed soil scientist. A simple hole test just indicates how your soil handles water for landscape drainage planning.
My hole is still full the next morning. What does that mean?
The soil in that spot will not absorb meaningful water. Plan on conveying water to an outlet rather than trying to infiltrate it there.
Does infiltration change with the seasons?
Yes, considerably. Clay that accepts water in a dry August can be effectively sealed in a wet February, so a winter test is the more conservative number.
Want this looked at on your property?
We give free, no-pressure on-site estimates across Denver, Mooresville, Cornelius, Davidson, Huntersville and Troutman.
