Free Calculator · Published October 2026
Well Recovery Rate Calculator for Specific Capacity
Enter casing diameter, drawdown, the pumping rate, and how fast the water rose after shutdown. The calculator returns a casing-refill rate and specific capacity so you can see whether a treatment train's backwash is even plausible.
Built by SubcontractorHub — the software plumbing contractors use to quote, finance, and run every job.
Book a DemoHow Fast Did the Well Come Back?
Specific capacity describes the test while the pump was running. Recovery rate here describes only the water that returned to the casing after it stopped.
Inside diameter from the well log. Nominal size is a guess if the log is missing.
Pumping water level minus static water level. Not the well depth.
The rate you actually pumped, measured, not the horsepower sticker.
How far the water rose toward static. Full recovery equals the drawdown.
Leave blank to skip. Use a backwash rate if you are sizing a filter.
📋 Important: All calculator results are ballpark estimates
The figures are approximate estimates from casing volume and the levels you type in. They vary with test length, season, and well condition. They are not a substitute for a sustained pump test read by a licensed well contractor. Always confirm static level, pumping level, and inside diameter on site.
Why Recovery Matters for Treatment and the Pump
Two different numbers
Specific capacity is pumping gallons per minute divided by feet of drawdown. It answers how hard the well had to be pulled to deliver the rate you ran. Recovery rate in this tool is narrower. After the pump stops, you time how many feet the water rises, convert those feet to gallons inside the casing, and divide by minutes.
The casing formula is mechanical: gallons per foot equals inside diameter in inches, squared, times 0.0408. A 6-inch casing holds about 1.47 gallons per foot. A 4-inch casing holds about 0.65. Using the wrong diameter does not make a small error. It scales with the square of the diameter. Neither number is a safe continuous yield. A hydrogeologist's pump test runs long enough to see whether the level stabilizes.
Worked examples
Same formulas as the calculator. They are illustrations, not a survey of typical wells.
| Test | Specific capacity | Casing refill |
|---|---|---|
| 6" casing, 8 gpm, 15 ft drawdown, full recovery in 20 min | 0.53 gpm/ft | 1.1 gpm |
| 6" casing, 10 gpm, 30 ft drawdown, full recovery in 45 min | 0.33 gpm/ft | 0.98 gpm |
| 5" casing, 7 gpm, 20 ft drawdown, 10 ft back in 15 min | 0.35 gpm/ft | 0.68 gpm |
Backwash is a sustained flow
A pressure tank can cover a shower for a minute. It cannot cover a ten-minute backwash. Iron filters, sediment backwash tanks, and acid neutralizers all ask the well for a flow the pump must hold, not a flow the tank stored earlier. If that flow is higher than anything the well demonstrated, the media will not lift and the equipment will be blamed for a well problem.
Size the pump and the tank with the well pump size calculator and the pressure tank sizing calculator. Then put the treatment stages in order with the well water treatment system selector. Recovery is the check that those stages have water to work with.
What a short test can miss
A well can look strong for ten minutes and keep falling for two hours. Seasonal water level, a clogged screen, and a pump set below its curve all change drawdown. Write static level, pumping level, rate, and the recovery timing on the job record so the next visit is compared with a measurement instead of a memory. A water treatment dealer who quotes a filter before that note is guessing at the backwash.
How to run the field steps
Measure the static level with the pump off and the system depressurized long enough for the level to sit still. Pump at a steady rate and record the pumping level once it stops dropping, or record that it never stopped. Drawdown is the difference. Shut the pump off, time the rise, and do not open fixtures while you time it. Then enter those four numbers here. If the level never stabilized, say so in the notes. The calculator cannot invent a stable drawdown you did not see.
Frequently Asked Questions
How do you calculate a well recovery rate?
A planning recovery rate is the gallons that returned to the casing after the pump stopped, divided by the minutes that rise took. Gallons per foot of casing equal the inside diameter in inches, squared, times 0.0408. Multiply by the feet the water rose, then divide by minutes. That number is only the water that refilled the pipe. It is not a certified safe yield.
What is specific capacity of a well?
Specific capacity is the pumping rate in gallons per minute divided by the drawdown in feet. Drawdown is the pumping water level minus the static water level. A well that pumps 10 gpm with 20 feet of drawdown has a specific capacity of 0.5 gpm per foot. The figure changes with how long you pump, the season, and how developed the well is. A short test is a planning number.
Why does well recovery matter for a water treatment system?
Iron filters, neutralizers, and other backwashing tanks need a sustained flow to lift the media, not a brief burst from a pressure tank. If the well cannot keep up with that backwash rate, the bed does not clean and the filter fails. Recovery and specific capacity tell you whether the well, not just the pump nameplate, can support the treatment train and the household peak.
Is the recovery rate the same as the safe pumping rate?
No. The recovery rate in this calculator is how fast the casing refilled after you stopped. The pumping rate you held during the test is the rate the well actually delivered while the level was down. A safe continuous yield is set by a longer test and by a licensed well contractor or hydrogeologist. Do not size a pump or a backwash on the casing-refill number alone.
What casing diameter should I enter?
Use the inside diameter of the casing, not the well depth and not the pump size. A nominal 6-inch casing is not always exactly 6 inches inside. If you know the inside diameter from the well log, use that. The gallons-per-foot figure changes with the square of the diameter, so a wrong diameter moves the recovery rate a lot.
Quote the Well and the Treatment Together
Keep the pump test, the tank settings, and the filter backwash on one customer record so the next tech is not starting from a blank page.
Get a Free DemoAll calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements. Recovery rate uses casing volume only. Specific capacity uses the pumping rate and drawdown you enter. Neither figure is a certified well yield.