A deep well pump is selected for conditions that exist while the well is pumping, not while it is resting. That is why dynamic water level - also called pumping water level - is normally the more important measurement for pump head, installation depth and dry-running protection. Static water level still matters, but mainly as the baseline used to calculate drawdown and evaluate how the well responds to pumping.
The practical rule is simple: use static water level to describe the resting well; use a stabilized dynamic water level measured at the required flow to select and install the pump. If the dynamic level is unknown, a pumping test should be completed before final pump selection.
What Is Static Water Level?
Static water level (SWL) is the vertical distance from a fixed reference point - normally the top of the well casing or the wellhead - to the water surface when the well is at rest.
A valid static measurement should be taken after pumping has stopped long enough for the water level to recover close to its normal equilibrium. The necessary recovery time varies. A productive well may recover quickly, while a low-yield well or a confined formation may take much longer. Record the rest period together with the measurement; a number described as static is less useful if the well had stopped only a few minutes earlier.
Static water level helps establish:
the starting groundwater level before pumping begins;
the baseline for calculating drawdown;
long-term or seasonal changes when measurements are repeated from the same reference point; and
whether a pumping test has recovered sufficiently after shutdown.
Static water level does not show how far the water will fall at the proposed pumping rate. Selecting a pump from SWL alone can therefore underestimate the actual lifting requirement and overestimate the water available above the pump.
What Is Dynamic Water Level?
Dynamic water level (DWL), often called pumping water level (PWL), is the distance from the same reference point to the water surface while the well is being pumped at a stated flow rate. The measurement is meaningful only when the flow rate and elapsed pumping time are also recorded.
Immediately after startup, the water level normally begins to fall. It may then stabilize when inflow to the well approximately balances the pumping rate, or it may continue declining throughout the test. For pump selection, the useful value is the stabilized pumping water level at the required duty flow. If the level never stabilizes, that result is itself a warning that the proposed flow may exceed the well's sustainable performance under the test conditions.
Dynamic water level is used to evaluate:
the vertical lift component of total dynamic head;
the depth required to keep the complete pump and motor assembly submerged;
the available submergence margin during operation;
the risk of vortexing, air entry, dry running or inadequate motor cooling; and
whether the selected pump flow is compatible with the well response.
Static Water Level vs Dynamic Water Level: The Key Difference
Static water level describes the well without pumping. Dynamic water level describes the well under a defined pumping load. The difference between them is drawdown.
Drawdown = Dynamic water level depth - Static water level depth
When depths are measured downward from the same point, the dynamic value is normally larger. For example, if SWL is 32 m below the casing reference and the stabilized PWL is 47 m at 20 m³/h, the drawdown is:
47 m - 32 m = 15 m of drawdown
The phrase 'dynamic water level' should not be treated as a permanent property of the well. It changes with pumping rate, pumping duration, aquifer conditions, nearby wells and season. A value measured at 10 m³/h cannot automatically be used to predict the level at 30 m³/h.
Which Water Level Should You Use for Deep Well Pump Selection?
Use the stabilized dynamic water level at the required flow rate as the operating reference. It affects three separate decisions.
1. Use Dynamic Water Level for the Vertical Lift
The vertical lift for a deep well system is normally measured from the pumping water level to the discharge elevation, not from the pump position and not from the static level. Pipe friction, fittings and required outlet pressure must then be added to determine total dynamic head.
For the full calculation method, see the existing Deep Well Pump Sizing Guide: Calculate Flow Rate and Total Dynamic Head. This article focuses on obtaining the correct water-level input for that calculation.
2. Use Dynamic Water Level to Plan Pump Installation Depth
The complete pump and motor assembly must remain adequately submerged under the lowest expected pumping level. The required margin is not one universal number: it depends on the pump and motor design, intake position, manufacturer requirements, water velocity around the motor, well geometry and seasonal decline.
Installation depth should be deep enough to maintain the specified submergence during the worst credible operating condition, but the unit should also remain safely above the well bottom and sediment zone. Do not place the pump deeper merely to increase head; pump head and installation depth are different parameters.
For that distinction, see Submersible Pump Head vs. Installation Depth: What Is the Difference?.
3. Use Dynamic Water Level to Check Well Yield and Dry-Running Risk
A pump can be hydraulically capable of producing a high flow while the well cannot supply that flow continuously. If extraction exceeds recharge, the water level may keep falling until the intake is exposed or the available submergence becomes too small. The result can be air entry, unstable flow, overheating, protective shutdowns or dry-running damage.
The selected duty flow should therefore be supported by pumping-test data. Oversizing the pump is not a substitute for confirming well yield.
How to Measure Static and Dynamic Water Levels
A qualified well contractor or hydrogeologist should design and interpret formal pumping tests, especially for municipal, industrial or high-value irrigation projects. The following field sequence explains the data that pump suppliers need.
Establish one reference point. Mark the top of casing or another fixed point and use it for every depth measurement. Record its height relative to ground level if elevations from different points will be compared.
Measure the static water level. Stop pumping and allow recovery. Record the water depth, date, time and duration since shutdown.
Start pumping at a measured, controlled rate. Use a flowmeter or another suitable method; do not estimate the flow from pipe size or pump nameplate alone.
Record water level against elapsed time. Take frequent readings soon after startup, then extend the intervals as the rate of change slows. Record the actual flow with each set of readings.
Determine whether the pumping level stabilizes. A stable or near-stable level at the target flow is more useful than a single reading taken immediately after startup.
Stop the pump and record recovery. Recovery measurements help confirm the well response and reveal whether the resting level returns to its earlier baseline.
Common measurement methods include an electric water-level tape, airline method, pressure transducer and acoustic meter. Suitability depends on well construction, depth, access, turbulence and the accuracy required. Whichever method is used, keep the reference point and units consistent.
How to Calculate and Interpret Well Drawdown
Drawdown shows how far the water level moves in response to pumping. A second useful indicator is specific capacity:
Specific capacity = Pumping rate / Drawdown
Using the earlier example, a well producing 20 m³/h with 15 m of drawdown has a specific capacity of:
20 m³/h ÷ 15 m = 1.33 m³/h per metre of drawdown
Specific capacity allows tests on the same well to be compared, provided the procedure, duration and measurement conditions are comparable. A declining value over time can indicate changes such as screen clogging, mineral deposition, sediment accumulation, aquifer stress or interference from nearby pumping. It does not, by itself, prove which cause is responsible.
Specific capacity is also not the same as a guaranteed sustainable yield. Long-term yield assessment may require constant-rate testing, step-drawdown testing, recovery analysis, seasonal data and hydrogeological interpretation.
Worked Example: Choosing the Correct Water Level
Assume a borehole project has these measured conditions:
well depth: 105 m;
static water level after recovery: 28 m below the casing reference;
A deep well pump is selected for conditions that exist while the well is pumping, not while it is resting. That is why dynamic water level - also called pumping water level - is normally the more important measurement for pump head, installation depth and dry-running protection. Static water level still matters, but mainly as the baseline used to calculate drawdown and evaluate how the well responds to pumping.
The practical rule is simple: use static water level to describe the resting well; use a stabilized dynamic water level measured at the required flow to select and install the pump. If the dynamic level is unknown, a pumping test should be completed before final pump selection.
What Is Static Water Level?
Static water level (SWL) is the vertical distance from a fixed reference point - normally the top of the well casing or the wellhead - to the water surface when the well is at rest.
A valid static measurement should be taken after pumping has stopped long enough for the water level to recover close to its normal equilibrium. The necessary recovery time varies. A productive well may recover quickly, while a low-yield well or a confined formation may take much longer. Record the rest period together with the measurement; a number described as static is less useful if the well had stopped only a few minutes earlier.
Static water level helps establish:
the starting groundwater level before pumping begins;
the baseline for calculating drawdown;
long-term or seasonal changes when measurements are repeated from the same reference point; and
whether a pumping test has recovered sufficiently after shutdown.
Static water level does not show how far the water will fall at the proposed pumping rate. Selecting a pump from SWL alone can therefore underestimate the actual lifting requirement and overestimate the water available above the pump.
What Is Dynamic Water Level?
Dynamic water level (DWL), often called pumping water level (PWL), is the distance from the same reference point to the water surface while the well is being pumped at a stated flow rate. The measurement is meaningful only when the flow rate and elapsed pumping time are also recorded.
Immediately after startup, the water level normally begins to fall. It may then stabilize when inflow to the well approximately balances the pumping rate, or it may continue declining throughout the test. For pump selection, the useful value is the stabilized pumping water level at the required duty flow. If the level never stabilizes, that result is itself a warning that the proposed flow may exceed the well's sustainable performance under the test conditions.
Dynamic water level is used to evaluate:
the vertical lift component of total dynamic head;
the depth required to keep the complete pump and motor assembly submerged;
the available submergence margin during operation;
the risk of vortexing, air entry, dry running or inadequate motor cooling; and
whether the selected pump flow is compatible with the well response.
Static Water Level vs Dynamic Water Level: The Key Difference
Static water level describes the well without pumping. Dynamic water level describes the well under a defined pumping load. The difference between them is drawdown.
Drawdown = Dynamic water level depth - Static water level depth
When depths are measured downward from the same point, the dynamic value is normally larger. For example, if SWL is 32 m below the casing reference and the stabilized PWL is 47 m at 20 m³/h, the drawdown is:
47 m - 32 m = 15 m of drawdown
The phrase 'dynamic water level' should not be treated as a permanent property of the well. It changes with pumping rate, pumping duration, aquifer conditions, nearby wells and season. A value measured at 10 m³/h cannot automatically be used to predict the level at 30 m³/h.
Which Water Level Should You Use for Deep Well Pump Selection?
Use the stabilized dynamic water level at the required flow rate as the operating reference. It affects three separate decisions.
1. Use Dynamic Water Level for the Vertical Lift
The vertical lift for a deep well system is normally measured from the pumping water level to the discharge elevation, not from the pump position and not from the static level. Pipe friction, fittings and required outlet pressure must then be added to determine total dynamic head.
For the full calculation method, see the existing Deep Well Pump Sizing Guide: Calculate Flow Rate and Total Dynamic Head. This article focuses on obtaining the correct water-level input for that calculation.
2. Use Dynamic Water Level to Plan Pump Installation Depth
The complete pump and motor assembly must remain adequately submerged under the lowest expected pumping level. The required margin is not one universal number: it depends on the pump and motor design, intake position, manufacturer requirements, water velocity around the motor, well geometry and seasonal decline.
Installation depth should be deep enough to maintain the specified submergence during the worst credible operating condition, but the unit should also remain safely above the well bottom and sediment zone. Do not place the pump deeper merely to increase head; pump head and installation depth are different parameters.
For that distinction, see Submersible Pump Head vs. Installation Depth: What Is the Difference?.
3. Use Dynamic Water Level to Check Well Yield and Dry-Running Risk
A pump can be hydraulically capable of producing a high flow while the well cannot supply that flow continuously. If extraction exceeds recharge, the water level may keep falling until the intake is exposed or the available submergence becomes too small. The result can be air entry, unstable flow, overheating, protective shutdowns or dry-running damage.
The selected duty flow should therefore be supported by pumping-test data. Oversizing the pump is not a substitute for confirming well yield.
How to Measure Static and Dynamic Water Levels
A qualified well contractor or hydrogeologist should design and interpret formal pumping tests, especially for municipal, industrial or high-value irrigation projects. The following field sequence explains the data that pump suppliers need.
Establish one reference point. Mark the top of casing or another fixed point and use it for every depth measurement. Record its height relative to ground level if elevations from different points will be compared.
Measure the static water level. Stop pumping and allow recovery. Record the water depth, date, time and duration since shutdown.
Start pumping at a measured, controlled rate. Use a flowmeter or another suitable method; do not estimate the flow from pipe size or pump nameplate alone.
Record water level against elapsed time. Take frequent readings soon after startup, then extend the intervals as the rate of change slows. Record the actual flow with each set of readings.
Determine whether the pumping level stabilizes. A stable or near-stable level at the target flow is more useful than a single reading taken immediately after startup.
Stop the pump and record recovery. Recovery measurements help confirm the well response and reveal whether the resting level returns to its earlier baseline.
Common measurement methods include an electric water-level tape, airline method, pressure transducer and acoustic meter. Suitability depends on well construction, depth, access, turbulence and the accuracy required. Whichever method is used, keep the reference point and units consistent.
How to Calculate and Interpret Well Drawdown
Drawdown shows how far the water level moves in response to pumping. A second useful indicator is specific capacity:
Specific capacity = Pumping rate / Drawdown
Using the earlier example, a well producing 20 m³/h with 15 m of drawdown has a specific capacity of:
20 m³/h ÷ 15 m = 1.33 m³/h per metre of drawdown
Specific capacity allows tests on the same well to be compared, provided the procedure, duration and measurement conditions are comparable. A declining value over time can indicate changes such as screen clogging, mineral deposition, sediment accumulation, aquifer stress or interference from nearby pumping. It does not, by itself, prove which cause is responsible.
Specific capacity is also not the same as a guaranteed sustainable yield. Long-term yield assessment may require constant-rate testing, step-drawdown testing, recovery analysis, seasonal data and hydrogeological interpretation.
Worked Example: Choosing the Correct Water Level
Assume a borehole project has these measured conditions:
well depth: 105 m;
static water level after recovery: 28 m below the casing reference;
