How to Calculate Drawdown in a Well

Water well drawdown occurs during groundwater withdrawal through the well screen. The natural water level in the aquifer depresses from the stress of the pumping in the aquifer and removal of the water. You can measure the water level in the well at different times to determine the drawdown that occurs during pumping activities. Some aquifers recharge more quickly than others; therefore, the drawdown in identical wells in different aquifers may not be the same. A few quick measurements will help you determine how much drawdown your well will exhibit over time.

Well with submersible pump
Electronic water level indicator
Notebook
Pen
Calculator

Instructions

- 1
  Insert the probe of the electronic water level into the well when the pump is at rest. Read the water level depth from the graduated tape when the electronic meter sounds a solid tone. This measurement is the static water level, which is the natural water level in the well.
- 2
  Record the static water level in your notebook.
- 3
  Turn the pump on and allow it to run.
- 4
  Measure the water level in the well at period intervals of five to 10 minutes and record the data in your notebook. As the pump runs, record both the time and value of the measurement. Continue to collect water level data until minimal change in the water level measurements exists.
- 5
  Subtract the measurements you collect as the pump is running from the static water level. The difference is the drawdown. For example, if the static water level is 1 foot below the top of the casing and the water level after one hour is 3 feet below the top of the casing, the drawdown at one hour of pumping is 2 feet. You can perform this calculation for any time after the start of pumping.

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