Run a percolation test with a bucket
Timebox: one afternoon of work spread over a day of waiting. Cost: a shovel, a bucket, a tape, water. Output: a number in inches per hour that decides whether your soil can take a swale or a dry well — or whether everything you were planning to bury should be piped instead.
Checked 2026-09-10 · procedure re-verified against sources below
What you need
- Shovel or post-hole digger
- Bucket or hose
- Measuring tape
- Watch or phone timer
- Four stakes or spray paint, to mark the holes
Steps
- Pick the spot. Test where the water will actually sit: the planned swale bottom or dry well location. Not the convenient corner of the lawn.
- Dig. One hole 6–12 inches wide, at least 12 inches deep. Rough sides are good; you want the native soil, not a glazed trench wall. Remove loose crumbs from the bottom.
- Presoak — twice. Fill the hole to the top and let it drain completely. Do it again. In clay the first fill may take half a day to leave. This step is the whole secret: a dry hole reads artificially fast, and the fast reading is the one people build on. See the unit-trap note for what you are actually measuring.
- Fill and time. Fill the hole to 12 inches above the bottom. Measure the water level, wait 30 minutes, measure again.
- Compute. Inches dropped in 30 minutes × 2 = inches per hour. Example: the level fell 0.4 in in 30 minutes → 0.8 in/hr.
- Repeat for the yard. One hole is a screen. For anything bigger than a small swale, run four holes across the area and write down all four numbers, with locations. The desk's method page says it plainly: one hole is not a yard.
Reading the result
| Your rate | Verdict |
|---|---|
| < 0.25 in/hr | Convey, don't soak. Pipe or basin with a real outlet. |
| 0.25–0.5 in/hr | Marginal. Shallow swale as carrier; no dry well. |
| 0.5–2 in/hr | Working range. Swales and modest dry wells behave — see the perk bands. |
| > 2 in/hr | Water leaves as it lands. Infiltration is easy; holding is the problem. |
Where people stop
- Skipping the presoak. The classic. A dry-season hole in clay reads 3 in/hr on day one and 0.3 on day two. The presoak is not optional ritual; it is the test.
- Testing through the topsoil. Two inches of imported loam over hardpan reads like a garden and behaves like a bathtub. Dig to the depth the water must penetrate.
- One hole, one verdict. Soil changes across a yard faster than opinions. Four holes.
Where to go next
- Percolation rate — what the bands permit.
- Size a swale — the number enters the plan.
- Measure grade — the other gate, 30 minutes.
Sources
- Minnesota Stormwater Manual, infiltration testing methods — stormwater.pca.state.mn.us
- USDA NRCS, soil survey and permeability — nrcs.usda.gov
- US EPA NPDES — epa.gov/npdes