Updated 2026-10-23
3 gpm or 30 gpm? How to read pump tests and define sustainable yield
Plan with the rate the well actually held through the pumping test, converted to m³ per day: 30 US gpm is about 164 m³/day, 3 gpm only about 16. WaterLocation forecasts the yield before drilling and checks it with the pumping test; tested results on its projects include 648 m³/day in Catalonia (official state test) and 864 m³/day (10 l/s) in Altmannstein, Bavaria.
Which number from the test is my sustainable yield?
Use the on‑site pumping test result that was actually maintained and recorded, and plan in m³ per day. This is the number WaterLocation uses in reports and in post‑drilling verification. Examples include 648 m³/day in Catalonia (confirmed by the official state test), about 200 m³/day in the Kalahari, more than 300 m³/day in Ulrichstein, and 864 m³/day (10 l/s) in Altmannstein.
If your sheet only shows a minute‑based number (e.g., in gpm), ask your driller to state the tested daily volume so you can compare it with your farm, resort or municipal demand.
How to read a pump test sheet without unit mix‑ups
- Identify the tested rate (the discharge the crew held during the test) and the unit used.
- For planning, write the same rate in m³ per day; this is how WaterLocation reports yields and compares them to demand.
- Keep the test record with the measured water level and rate together; this is the reference for pump sizing and operating limits.
- Before drilling, a survey can state the forecast yield in m³/day; the pumping test then compares the real yield with the forecast. See predict borehole yield.
Quick unit conversion
| Pump test figure | Per day |
|---|---|
| 3 US gpm | ≈ 16 m³/day |
| 30 US gpm | ≈ 164 m³/day |
| 1 litre per second | 86.4 m³/day |
| 10 litres per second | 864 m³/day |
1 US gallon = 3.785 litres; a day has 1,440 minutes.
Tested yields from real sites
| Site | Before | Tested result | Yield |
|---|---|---|---|
| Catalonia, Spain (deep clay) | Several failed boreholes | Water at 136 m; state test | 648 m³/day |
| Altmannstein, Germany (limestone) | Old well 2 l/s; needed 10 l/s | Water at 88 m | 864 m³/day (10 l/s) |
| Ulrichstein, Germany (basalt) | All earlier boreholes failed; demand 260 m³/day | ≈200 m well; static level 87 m | 300+ m³/day |
| Kalahari, South Africa (rock and quartz) | 25 boreholes; 4 steady | 150 m; static level 28 m | ≈200 m³/day |
| Namibia, Kalahari (dolomite) | 9 wells; 1 steady year‑round | Two new wells at 21 m and 57 m | 100 and 350+ m³/day |
| Mitterfirmiansreut, Germany (granite) | 4 empty holes up to 118 m | Water at 22 m | 200 m³/day |
What if the test and my target don’t match?
- Survey before redrilling: on sites with dry or low‑yield holes, a fracture survey can site a new point with a forecast yield and depth. See dry borehole: what next and borehole siting methods.
- Result verification: WaterLocation ties its discovery fee to the pumping test result; if a borehole drilled at the specified point and depth doesn’t deliver, there is no discovery fee. See pay only if water is found.
- Hard‑rock caution: in granite, basalt and dolomite, yield depends on narrow fractures; a hole a few metres off can underperform. See hard‑rock borehole yield.
There are no guaranteed results; every site is different and yields are quoted per site.
Sources
Questions
What unit should I plan with: gpm or m³/day?
WaterLocation plans and reports in m³ per day. To convert: multiply US gpm by 5.45 to get m³/day (30 gpm ≈ 164 m³/day), or litres per second by 86.4 (10 l/s = 864 m³/day).
How is yield confirmed?
By an on‑site pumping test compared with the forecast; in Catalonia the official state pumping test confirmed 648 m³/day.
Can you estimate sustainable yield before drilling?
Yes. A survey report gives the point, depth and forecast m³/day; the pumping test then compares the real yield with the forecast.