Well depth, water level and sustainable yield describe different things. You need all three before selecting equipment.
1. Investigate before choosing a depth
Nearby borehole logs are useful evidence about geology and water-bearing layers, but they do not guarantee the same result on your plot. Obtain local records and discuss drilling targets with a licensed driller or hydrogeologist. Include access for the rig and possible sources of contamination in the site plan.
Pumping lowers the water level around a well. A level that looks adequate when the pump is off may fall towards the intake during use. Seasonal changes also matter. A deeper hole alone does not prove adequate yield or safe water.
USGS · Groundwater wells ↗2. Keep a pumping-test record
Use a consistent reference point for every water-level measurement. Record static water level before pumping, pumping rate, elapsed time, pumping level and recovery after stopping. Have a well professional perform the test and interpret the result; keep sanitary well components closed and protected.
Drawdown is pumping level minus static level when both depths are measured downward from the same datum. Specific capacity is test flow divided by drawdown. It describes the observed test conditions; it does not establish a long-term abstraction limit. Our well tool makes that distinction explicit.
3. Compare daily demand with peak demand
A daily budget is a volume. Two showers running together create an instantaneous flow requirement. A well may produce enough total water in a day yet need buffer storage to meet short peaks. Storage cannot fix a source that consistently supplies less than total demand.
For a rough first budget, multiply residents by an explicit litres-per-person assumption and add irrigation or other uses separately. Replace the assumption with metered readings when available. Include filter backwash demand if the treatment equipment requires it.
4. Confirm water quality separately
CDC advises annual well testing for coliform bacteria, nitrate, total dissolved solids and pH, with additional tests selected for local risks. Use a certified laboratory and its sampling instructions. Test again when flooding, repairs or a change in water characteristics raises concern.
A water-level or yield test does not establish potability. If a laboratory reports harmful contamination, arrange a safe drinking-water source and ask the local health authority to interpret the result.
CDC · Testing well water ↗What the well report should tell you
| Record | What it means | Why you need it |
|---|---|---|
| Total drilled depth | Bottom of the borehole | Construction record, not water yield |
| Static level | Resting water surface | Baseline for drawdown |
| Pumping level + rate + time | Water level under a known load | Pump selection and test interpretation |
| Recovery record | Water-level rebound after pumping | Evidence for professional yield assessment |
| Laboratory report | Measured water quality | Treatment and drinking-water decisions |
Worked example
A pumping-test snapshot
Static level is 12 m below the datum. At 20 L/min, the pumping level is 18 m.
Drawdown = 18 − 12 = 6 m Specific capacity = 20 / 6 = 3.33 L/min/m
This is a snapshot at the recorded test duration. For pump head, use the pumping water level, delivery elevation, required pressure and friction losses—not total borehole depth.
What to have ready
- Drilling log and well construction details
- Dated pumping and recovery test
- Daily and simultaneous water demand
- Certified raw-water analysis
Common mistakes
- Buying a pump from total well depth alone.
- Using a short bucket test as a sustainable yield guarantee.
- Assuming clear water is safe water.
Reference check: 5 September 2026. Sources include US public agencies. Principles are general; regulations and design values must be checked where you live.Worked examples use stated hypothetical inputs.