# How to Calculate a Private Well Recovery Rate from a Pump Test

Source: https://brictale.com/water/wells/calculate-private-well-recovery-rate
Published: 2026-08-27
Audience: Homeowner
Published by Brictale, a consumer home-intelligence publication. https://brictale.com

## Short answer

Recovery rate is the water-level rise after pumping stops, converted to gallons per minute using the actual casing inside diameter. Subtract each later depth-to-water from the prior depth, multiply the recovered feet by casing gallons per foot, and divide by elapsed minutes. Treat the result as an estimate, not a universal pass/fail number: compare only like-for-like records and use local guidance or a qualified well professional for a formal yield decision.

---

# How to Calculate a Private Well Recovery Rate from a Pump Test

If you have a well test record, calculate recovery from the water level inside the well after pumping stops—not from the pump's discharge rate and not from the pressure tank's usable volume.

Use this sequence:

1. Keep every water-level reading tied to the same datum, normally the top of the well casing.
2. Confirm whether each number is a depth to water, a water-level elevation, or a stated amount of rise.
3. Confirm the casing's actual inside diameter for the water column being measured.
4. For each interval, multiply the water-level rise in feet by the casing's gallons per foot, then divide by elapsed minutes.
5. Plot the interval results and compare the recovery record with the pumping record only when the tests used comparable conditions.

The result is an estimate of water returning to the well during that interval. It is not automatically the well's sustainable yield, the pump's capacity, or a national “good recovery rate.” A complete, comparable record can support a household-demand or storage discussion. A missing datum, unknown casing diameter, contradictory record, very slow recovery, or a test that could have run the pump dry is a reason to stop calculating and ask a qualified well professional for a controlled evaluation.

## 1. Put the number in the right category

The most important calculation is deciding what you are actually calculating. A private-well report can contain several rates and levels that look interchangeable but answer different questions.

### Recovery rate

Recovery rate is the rate at which the water level rises after pumping has stopped. On a typical report, water depth is measured downward from the top of casing. As the water rises, the depth number gets smaller. If the depth is 210 feet immediately after shutdown and 170 feet 60 minutes later, the water level rose 40 feet in that interval.

The Massachusetts Department of Environmental Protection describes recovery this way and shows the same conversion: water-column rise multiplied by gallons per foot of casing, divided by elapsed minutes. [Massachusetts’ private-well yield guidance explains the recovery definition and worked arithmetic](https://www.mass.gov/doc/estimating-private-well-yields-0/download). The word “rate” matters: one reading at shutdown and one reading the next day tell you how far the water came back, but they do not show how the rate changed along the way.

### Pump discharge rate

Pump discharge is the water leaving a discharge pipe during pumping, usually recorded in gallons per minute. It describes the withdrawal rate imposed during the test. It may be measured with a meter, a calibrated container and timed volume for a controlled professional test, or another test method. It is not the rate at which water is entering the well from the aquifer.

New York defines well yield as a sustainable quantity that may flow from or be pumped continuously from a well. [New York’s Appendix 5B definition of well yield](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm) is why a short discharge reading should not be relabeled “recovery” or “sustainable yield.” A pump can discharge faster than the formation supplies water for a while by using water already stored in the casing.

### Drawdown and pumping level

Drawdown is the change from the static water level to the lower water level while the pump is running. If static depth is 80 feet and pumping depth is 200 feet, drawdown is 120 feet. It is a level change, not a flow rate. “Pumping level” usually means the depth reached during pumping, while “drawdown” is the difference between levels.

New York calls a stabilized water level the steady state achieved during constant-rate withdrawal and defines static water level as the natural level when the well is not pumping or has fully recovered. [Those definitions appear in Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm). Use one reference point for every reading; switching between ground surface and casing top can create a false recovery.

### Pressure-tank drawdown

Pressure-tank drawdown is the amount of usable water delivered from the tank between pressure-switch cut-in and cut-out, or the volume observed during a tank test. It describes the plumbing system's buffer. It does not measure aquifer recovery.

The tank can make a low-yield well feel normal for a short period, and a small usable tank can make a healthy well pump frequently. Connecticut's private-well guidance warns that pressure tanks have little usable volume compared with their total tank size and discusses short cycling as a pump-life concern. [Connecticut’s guidance separates pressure storage from well capacity](https://portal.ct.gov/dph/-/media/departments-and-agencies/dph/dph/environmental_health/private_wells/28privatewellguidancefordeterminingwellsafeyieldpdf.pdf?hash=002EC717EB075442072922C7F6AC95C4&rev=b07c25d4dc3c4e879a8b6ef4ad9c002d). Do not put a pressure-tank number into the recovery formula.

| Record field | What it tells you | What it does not prove |
| --- | --- | --- |
| Static water level | Starting water depth after rest or full recovery | The sustainable yield |
| Pumping level / drawdown | How far the level fell during withdrawal | The pump's discharge rate |
| Pump discharge | The withdrawal rate imposed at the outlet | Aquifer inflow or recovery |
| Pressure-tank drawdown | Usable plumbing-system storage | Well recovery or casing storage |
| Recovery readings | Water-level rebound after shutdown | A universal pass/fail rate |

{{visual:recovery-curve-definition}}

## 2. Sort the test record before doing arithmetic

Do not begin with a calculator. Begin with a record audit. A defensible result needs the identity of the well, the test conditions, and a time series.

### Minimum fields to find

Look for these fields on a completion report, pump-test sheet, inspection packet, or driller's invoice:

- well address or identifier and test date;
- test method, such as constant-rate pump, variable-rate pump, air lift, bailing, or slug;
- static depth to water and the reference point used;
- discharge rate and whether it stayed constant;
- pumping depth or maximum drawdown;
- pump duration;
- the exact time pumping stopped;
- recovery readings with clock time or elapsed minutes;
- casing inside diameter, screened or open-borehole configuration, and any change in casing diameter;
- whether the discharge was sent away from the well rather than allowed to return near it.

Massachusetts’ Model Board of Health Regulations for Private Wells use a pumping-test report to document the well-test method, static level, flowing or discharge rate, pumping level, pumping and recovery durations, and recovery water level. [The MassDEP model regulation identifies those report fields](https://www.mass.gov/doc/model-board-of-health-regulations-for-private-wells/download). That list is useful even outside Massachusetts because it exposes the fields needed to judge comparability; it is model and local guidance, not a nationwide reporting form.

### Translate the notation

Write a small key at the top of your worksheet:

- `BGS` or `ft below ground surface` means a depth down from ground surface.
- `TOC` or `top of casing` means a depth down from the casing rim.
- `water elevation` means a height relative to a survey datum; higher elevation means a higher water level, so its subtraction direction is different.
- `recovered 40 ft` means a rise amount, not necessarily a depth-to-water reading.

If the record says “recovery: 120 ft in 1 hour,” do not assume it means the depth to water was 120 feet. The Massachusetts explainer calls out this exact ambiguity and recommends clarifying what the driller wrote. [Read the Massachusetts discussion of recovery notation before interpreting a single number](https://www.mass.gov/doc/estimating-private-well-yields-0/download).

### Mark a record as non-comparable

Put a clear “do not compare” mark on the sheet when any of these are true:

- static and recovery readings use different reference points;
- the test method or discharge rate changed without a new time segment;
- the pump stopped or restarted during the supposed constant-rate test;
- a pressure-tank observation is being compared with a well-casing recovery;
- casing diameter is nominal, guessed, or different from the water column being measured;
- water was discharged where it could flow back toward the well;
- the well was pumped dry, the pump lost prime, a low-water cutoff operated, or the record does not say what happened;
- recovery was interrupted by household water use, another well, irrigation, or a power outage;
- the record has only a final “recovered” statement and no time-stamped readings.

These flags do not mean the well is bad. They mean the number cannot carry the conclusion you want to place on it. New York's yield-test performance requirements call for water-level and flow observations before pumping, at cessation, and periodically during drawdown and recovery, and call for discharge that avoids short-circuiting back into the aquifer. [See the test-record and discharge provisions in Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm).

## 3. Calculate gallons per minute from actual casing diameter

The short formula is:

`interval recovery gpm = recovered feet × casing gallons per foot ÷ elapsed minutes`

For a full circular casing, estimate gallons per vertical foot from the actual inside diameter in inches:

`casing gallons per foot ≈ 0.0408 × (inside diameter in inches)²`

This is geometry: the circle's area times one foot of length, converted to gallons. MassDEP's water-quantity table lists 1.469 gallons per foot for a 6-inch diameter, which is the reference value the rounded coefficient reproduces. [See the MassDEP gallons-per-foot table](https://www.mass.gov/doc/private-well-guidelines/download). The conversion assumes the measured rebound represents water-column movement inside a uniform cylindrical segment. It is not a claim that every well's aquifer inflow is uniform or that every open borehole behaves like a storage cylinder.

### Why the actual inside diameter matters

“Six-inch well” is often a useful shorthand, but the casing's actual inside diameter can differ from nominal size, and the water column may include more than one casing diameter. A small diameter error is squared in the formula. For a 6-inch inside diameter, the result is about 1.47 gallons per foot, commonly rounded to 1.5 gallons per foot in state homeowner guidance. [New York’s water-storage fact sheet gives the 1.5-gallon-per-foot approximation for a typical 6-inch casing](https://healthweb-back.health.ny.gov/environmental/water/drinking/regulations/fact_sheets/fs2_water_storage.htm).

If the record gives a 5.5-inch actual inside diameter:

`0.0408 × 5.5² = 1.23 gallons per foot`

If the casing changes from 6 inches to 4 inches across the measured interval, do not apply one number to the entire rise. A professional should divide the water-column movement into segments or use the well construction record and test method to determine what volume is relevant. If the well is a large-diameter bored well, has a screen, or has an uncased open-rock interval, the simple casing-cylinder estimate may be a rough storage conversion rather than a reliable aquifer-yield result.

### Work one interval at a time

For depth-to-water readings, calculate the rise as:

`recovered feet = earlier depth − later depth`

Use elapsed minutes, not the wall-clock hour label. Suppose a 6-inch casing has these readings:

| Reading | Elapsed time after pump stop | Depth to water |
| --- | ---: | ---: |
| Shutdown | 0 minutes | 200 ft |
| Recovery 1 | 30 minutes | 160 ft |
| Recovery 2 | 90 minutes | 120 ft |
| Recovery 3 | 180 minutes | 100 ft |

With 1.47 gallons per foot:

- 0–30 minutes: `(200 − 160) × 1.47 ÷ 30 = 1.96 gpm`.
- 30–90 minutes: `(160 − 120) × 1.47 ÷ 60 = 0.98 gpm`.
- 90–180 minutes: `(120 − 100) × 1.47 ÷ 90 = 0.33 gpm`.
- 0–180 minutes overall: `(200 − 100) × 1.47 ÷ 180 = 0.82 gpm`.

All four numbers can be true at once. The early recovery is faster; the rate slows as the water level approaches the starting level. That is why a single “recovery rate” without an interval is incomplete. Record both interval rates and the cumulative rate.

### If the report gives a water-level rise already

If the report says the water rose 40 feet in 60 minutes and the relevant casing inside diameter is 6 inches:

`40 × 1.47 ÷ 60 = 0.98 gpm`

If it says the depth changed from 210 feet to 170 feet, the rise is also 40 feet. If it says water elevation changed from 600.0 feet to 640.0 feet, the rise is 40 feet directly. Do not subtract elevations in the same direction as depths without first identifying the measurement type.

The number is an estimate of water-column recovery. New York's definition of sustainable yield and its requirement for an extended, stabilized test are the reason to keep that limitation visible. [New York describes the purpose of a yield test as evidence of sustainable flow over an extended period](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm).

## 4. Use a safe observation boundary

For most homeowners, the safest use of this worksheet is to read an existing test record and ask a professional to collect missing data. A recovery test can involve running a pump for hours, discharging water, measuring inside the well, and managing electrical and pressurized equipment. That is not a casual faucet test.

### What you may safely document

Without opening equipment, you can generally:

- photograph or transcribe an existing completion report;
- note the well tag, date, stated casing size, stated test method, and stated times;
- observe whether water is clear, sandy, or discolored at an approved discharge point without touching the water if local conditions make that unsafe;
- record the household symptom: low flow, air sputter, pump running continuously, or water returning after a dry period;
- read a plainly visible, installed flow totalizer or pressure gauge without removing a cover or changing a setting;
- keep a log of normal and abnormal pump run times from the outside of the equipment;
- stop water use and call a professional if the pump runs continuously, the water becomes sandy, the well runs dry, or the system loses pressure.

### What not to do for this calculation

Do not open a well cap, casing, pitless adapter, pressure-tank port, pump control box, or electrical enclosure as part of a DIY recovery test. Do not insert a tape, probe, airline, or cable into a well unless a qualified well professional has established a safe, sanitary, equipment-compatible method for that specific well. Do not pull a pump, open the casing, enter a well pit or confined space, test live wiring, bypass a low-water cutoff, or manipulate a pressure switch or pressurized tank.

Do not run a pump for an improvised “until it goes dry” test. You may lose water service, draw sediment into the system, overheat or damage equipment, or create a result that says more about a disturbed well than about normal supply. If the test would require an electrical cover to be open, stop. OSHA's workplace standard says exposed live parts should be deenergized before work, unverified deenergized parts are treated as energized, and only qualified persons may work on energized parts. [OSHA 1910.333 provides that electrical safety boundary](https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.333); it is not a homeowner licensing rule, but it is a conservative reason to leave energized controls to qualified professionals.

New York's well standard also requires protected, sanitary well components and describes approved ways professionals may measure water level, including an electric sounder or pressure transducer. [The measurement-method and well-protection provisions are in Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm). That does not turn an unplanned homeowner insertion into a safe procedure.

### Stop immediately when the record signals risk

Stop the household observation and call a well contractor or pump professional if:

- the pump does not shut off;
- the water level is near the pump intake or the system trips a low-water protection device;
- water becomes sandy, cloudy, or suddenly changes color;
- the well has recently flooded, been opened, hydrofractured, chemically treated, or repaired;
- there is exposed wiring, a wet electrical area, a damaged well cap, or a missing sanitary seal;
- the well is in a pit, crawlspace, vault, or other area where entry could be a confined-space hazard;
- recovery is being used to decide whether to sell a house, size a new pump, drill deeper, or approve a high-demand use.

If a well runs dry and comes back, or if work has been done on the well, treat water quality as a separate decision. [Maine CDC recommends testing private-well water after a well runs dry and returns and after work is done](https://www.maine.gov/dhhs/mecdc/healthy-living/health-and-safety/drinking-water-safety/private-well-water). Recovery tells you about water-level behavior, not whether the water is safe to drink.

## 5. Read the recovery curve and test comparability

The worksheet should produce a curve, even if you draw it by hand. Put elapsed time on the horizontal axis and depth to water on the vertical axis, with deeper readings lower on the page. The curve should move upward after shutdown as the depth decreases.

### What the shape can tell you

- A steep early rise that flattens is common in a recovery record. Report the interval rates rather than averaging away the change.
- A nearly flat line means little measured rebound during that interval. Check the datum, units, elapsed time, pump status, and whether another use interrupted recovery before concluding the well is slow.
- A sudden jump in depth may be a transcription error, a different reference point, a disconnected gauge, or a real event. Mark it as questionable and ask for the original field notes.
- A recovery curve that never approaches the prior static level within the recorded window is incomplete information unless the test duration and local criterion say otherwise. Do not call it “failed” from the graph alone.
- Recovery that looks strong but conflicts sharply with the discharge test may indicate casing storage, a changing discharge rate, bad timing, a miswritten depth, or a different test method.

Massachusetts guidance says recovery and pumping-test estimates should roughly agree when the data were recorded accurately, and it recommends asking the driller to explain a wild discrepancy. [Use the Massachusetts comparison warning when checking a report](https://www.mass.gov/doc/estimating-private-well-yields-0/download).

### Compare like with like

Before comparing a recovery estimate with a pump discharge, write these side by side:

| Comparison question | If the answer is no |
| --- | --- |
| Was the same well tested? | Do not compare the records. |
| Was the static level measured after a similar rest period? | Label seasonal or recovery-state differences. |
| Was discharge constant, or were step rates identified? | Compare only within matching segments. |
| Was pump shutdown time recorded exactly? | Recalculate only after timing is clarified. |
| Is casing inside diameter known for the measured interval? | Use a professional estimate, not nominal size. |
| Was discharge kept away from the well? | Treat possible recirculation as a confounder. |
| Were readings taken with the same datum and units? | Reconcile the datum first. |
| Was household use stopped during recovery? | Mark the recovery as interrupted. |

Even a technically correct calculation can be misleading if the test is not comparable. For example, a 2-gpm discharge during a short test and a 0.8-gpm three-hour cumulative recovery estimate do not automatically mean the pump is oversized. The first is a withdrawal rate; the second is an average rebound over a selected interval. They may be describing different portions of the system.

### Do not turn a regional table into a national benchmark

There is no single U.S. homeowner threshold that makes every well “good.” Geology, depth, casing, storage, season, household demand, local rules, and test duration all matter.

Maine publishes one regional example: recommended minimum recovery rates for single-family homes tied to well depth, from 5 gpm at 75 feet to 0.5 gpm at 420 feet. The table states that it assumes a static level of approximately 25 feet below ground surface and about 1.5 gallons per foot in a 6-inch well. [Read Maine’s Section 407 recovery table with its stated assumptions](https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/SECTION-407-Recovery-Rates.pdf). It is not a national residential benchmark, and it is not a substitute for your jurisdiction's rule or a controlled test.

New York uses a different frame for a standard test: recovery to at least 90 percent of the initial water level or 24 hours, with failure to reach that recovery after 24 hours potentially indicating that the tested flow is not sustainable for an extended period. [That criterion appears in New York’s Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm). Massachusetts’ explanatory material discusses an older 85-percent-within-24-hours rule of thumb. [See the Massachusetts qualification around that rule of thumb](https://www.mass.gov/doc/estimating-private-well-yields-0/download). The differences are exactly why Brictale treats these as labeled regional guidance, not one national answer.

## 6. Turn the result into the next household decision

The recovery number is useful only when connected to the problem you are trying to solve. Choose the next action from the quality of the record, the shape of recovery, and the household symptom.

| What your worksheet shows | What it supports | Safest next action |
| --- | --- | --- |
| Complete timed readings, known inside diameter, consistent datum, no interruption | Transparent interval and cumulative estimates | Save the calculation, plot the curve, and ask a professional to interpret it alongside the full pump test. |
| Recovery estimate and discharge estimate are broadly similar under comparable conditions | A plausible record, not a guarantee | Compare with local guidance and actual peak demand; do not resize the pump from recovery alone. |
| Recovery and discharge differ sharply | A record-quality or casing-storage question | Ask the driller for field notes, discharge method, casing dimensions, and an explanation before making equipment decisions. |
| Recovery data are missing, untimed, or ambiguous | No defensible calculation | Request the completion report or a controlled professional test. |
| Slow or incomplete recovery plus low flow during simultaneous household use | A capacity-versus-demand problem may exist | Have a qualified professional evaluate demand, pump setting, controls, storage, and local options. |
| Water-quality change after a dry period or well work | A separate health and sanitary question | Stop treating recovery as proof of safety; arrange appropriate laboratory testing. |

### Daily demand is not peak flow

A well can produce enough water over a day but fail when a shower, washer, toilet, and outdoor use overlap. New York’s fact sheet says household daily usage and peak demand are different, gives 5 gpm as an estimate of typical peak demand, and notes that low-yield wells may need supplemental storage to meet peak demand. [Read New York’s demand-versus-storage explanation](https://healthweb-back.health.ny.gov/environmental/water/drinking/regulations/fact_sheets/fs2_water_storage.htm). That is New York guidance, not a universal design target.

Write down your real peak pattern:

- number of occupants and bedrooms;
- simultaneous showers or baths;
- washer and dishwasher overlap;
- irrigation, hose, pool, spa, or livestock use;
- treatment equipment regeneration;
- whether the symptom is low pressure, no water, pump cycling, or a pump that never shuts off.

Then bring both columns to a professional: “water the well returns” and “water the house asks for.” A storage tank, demand scheduling, a control adjustment, a pump repair, a well rehabilitation, or a new source can have very different risk and cost implications. Recovery alone cannot choose among them.

### Storage is a design discussion, not a DIY add-on

New York publishes storage recommendations by yield and bedroom count for its own homeowner context, and advises consulting water-well professionals when use is higher than typical or when casing storage is being considered. [Use the New York storage table only with its local scope and assumptions](https://healthweb-back.health.ny.gov/environmental/water/drinking/regulations/fact_sheets/fs2_water_storage.htm). Connecticut also discusses above-ground storage and notes that it can remain available during a power outage, while pressure tanks have relatively little usable volume. [See Connecticut’s storage discussion](https://portal.ct.gov/dph/-/media/departments-and-agencies/dph/dph/environmental_health/private_wells/28privatewellguidancefordeterminingwellsafeyieldpdf.pdf?hash=002EC717EB075442072922C7F6AC95C4&rev=b07c25d4dc3c4e879a8b6ef4ad9c002d).

Do not add a tank, alter pressure settings, bypass protection, or change a pump based on a spreadsheet result. Storage must be sized for the actual system, treatment equipment, booster arrangement, sanitation, freeze protection, drainage, controls, and power-loss behavior.

## 7. Prepare a professional handoff when the number matters

If the result will affect a home purchase, a pump replacement, a new bathroom, irrigation, a storage installation, or a claim that a well is failing, your goal is not to sound certain. Your goal is to hand over a clean record that lets the professional identify what is known and what is missing.

### Give the professional this packet

Include:

1. the completed worksheet and the source document;
2. the well completion report, well log, pump model and setting if known;
3. static, pumping, and recovery readings with units and datum;
4. actual casing inside diameter or the record used to identify it;
5. discharge rate, how it was measured, and where water was discharged;
6. test start, pump-stop, and every recovery timestamp;
7. household symptoms and dates, including drought, flooding, repairs, hydrofracturing, treatment changes, or a well running dry;
8. water-quality results and any recent work invoices;
9. the decision you need to make, such as “Can this serve four people with no irrigation?” rather than “Is 1 gpm good?”

Connecticut describes a professional approach for an older home that uses a low-capacity meter on the discharge line and runs the well to daylight until the discharge stabilizes. [That professional-meter example is in Connecticut Publication No. 28](https://portal.ct.gov/dph/-/media/departments-and-agencies/dph/dph/environmental_health/private_wells/28privatewellguidancefordeterminingwellsafeyieldpdf.pdf?hash=002EC717EB075442072922C7F6AC95C4&rev=b07c25d4dc3c4e879a8b6ef4ad9c002d). The point is not to reproduce that test casually; it is to ask for a controlled method and a stabilized result when a decision requires more than a record calculation.

### Questions worth asking

- What test method was used, and was the discharge constant?
- Was the well ever pumped dry or below the pump intake?
- Does the recovery interval represent casing storage, aquifer inflow, or both?
- Is the casing diameter an actual inside diameter, and does it change below the pump?
- Are the recovery and discharge records comparable enough to use together?
- What local or state criterion applies to this well and intended use?
- What demand was assumed, and does it include simultaneous fixtures or irrigation?
- Would storage solve a peak-demand problem without masking a pump, control, or water-quality problem?
- What would a controlled retest measure, for how long, and where would discharge go?

## 8. Print, calculate, and preserve the record

Use the companion [Private Well Recovery Measurement Sheet](downloads/private-well-recovery-measurement-sheet.pdf) for the fields below. It is a homeowner record, not an official inspection, code form, laboratory report, or professional yield certification.

### Header

- Property / well identifier: ______________________________
- Test date: __________________  Source of record: __________________
- Test method: __________________  Professional / company: __________________
- Reference datum: ☐ top of casing  ☐ ground surface  ☐ water elevation datum
- Casing actual inside diameter: ______ in  Casing segment / notes: __________________
- Pump discharge: ______ gpm  Pumping duration: ______  Recovery observation duration: ______
- Static depth / elevation: ______  Pumping depth / elevation: ______

### Recovery log

| Clock time | Elapsed minutes after pump stop | Depth to water or elevation | Rise from prior reading | Casing gallons per foot | Interval recovery gpm | Notes |
| --- | ---: | ---: | ---: | ---: | ---: | --- |
|  | 0 |  | — |  | — |  |
|  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |

For a known, uniform inside diameter, calculate gallons per foot as `0.0408 × ID²`. For depth readings, calculate rise as `earlier depth − later depth`. Then calculate interval gpm as `rise × gallons per foot ÷ minutes since the prior reading`. If the reading is a water elevation, use the elevation increase as the rise. If the diameter, datum, test method, or pump status is uncertain, leave the calculation blank and mark “professional review.”

### Plotting grid

Use this small grid as a plotting aid: put elapsed minutes across the top and depth to water down the side. Because depth is measured downward, smaller depth values belong higher on your graph. Mark the exact reading even if it falls between rows, then connect the points in time order. For the worked example above, the points are 200 feet at 0 minutes, 160 feet at 30, 120 feet at 90, and 100 feet at 180; those points should form a rising curve on the page.

| Depth to water (ft) / elapsed min | 0 | 30 | 60 | 90 | 120 | 150 | 180 |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 200 |  |  |  |  |  |  |  |
| 180 |  |  |  |  |  |  |  |
| 160 |  |  |  |  |  |  |  |
| 140 |  |  |  |  |  |  |  |
| 120 |  |  |  |  |  |  |  |
| 100 |  |  |  |  |  |  |  |

### Comparability and safety checklist

- ☐ Same well and same test date identified.
- ☐ Static reading and every recovery reading use the same datum.
- ☐ Units are clear: feet, minutes, and gpm.
- ☐ Actual casing inside diameter is documented, not guessed from a nominal label.
- ☐ Pump-stop time is known.
- ☐ Discharge rate and measurement method are recorded.
- ☐ Discharge was kept away from the well where the record says so.
- ☐ Recovery was not interrupted by household use, irrigation, another well, or power loss.
- ☐ No pump-dry event, low-water cutoff, sand event, or unexplained pressure loss occurred.
- ☐ No well cap, energized control, wiring, pump, pressure vessel, or confined space was opened or manipulated by the homeowner.
- ☐ Local guidance was identified before using any threshold.
- ☐ Water-quality testing was considered separately after dry-well return, flooding, or well work.

Keep the sheet with the well log, invoices, pump information, and water tests. A clean record becomes more valuable over time because it gives the next professional a baseline—and because it keeps a rough homeowner calculation from being mistaken for a certified yield test.

## Evidence

- [New York State Department of Health — Part 5, Subpart 5-1 Standards for Water Wells, Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm) — New York drinking-water well construction and yield-test standard; definition used here to explain measurement datum, not as a national rule.
- [New York State Department of Health — Part 5, Subpart 5-1 Standards for Water Wells, Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm) — New York drinking-water well construction and yield-test standard; distinguishes sustainable yield from a short observation.
- [New York State Department of Health — Part 5, Subpart 5-1 Standards for Water Wells, Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm) — New York standard for new and redeveloped wells; the article uses the recording principles for worksheet design and labels the state-specific duration and recovery criteria.
- [New York State Department of Health — Part 5, Subpart 5-1 Standards for Water Wells, Appendix 5B](https://healthweb-back.health.ny.gov/regulations/nycrr/title_10/part_5/appendix_5b.htm) — New York standard only, not a universal residential pass/fail threshold.
- [Massachusetts Department of Environmental Protection — Estimating Private Well Yields using DEM’s Well](https://www.mass.gov/doc/estimating-private-well-yields-0/download) — Massachusetts homeowner and well-record guidance; the article uses the definition and arithmetic as a transparent calculation method, not as a universal yield test.
- [Massachusetts Department of Environmental Protection — Estimating Private Well Yields using DEM’s Well](https://www.mass.gov/doc/estimating-private-well-yields-0/download) — Massachusetts explanatory guidance; applies as a comparability warning for homeowner records.
- [New York State Department of Health — Individual Water Supply Wells, Fact Sheet #2: Water Storage](https://healthweb-back.health.ny.gov/environmental/water/drinking/regulations/fact_sheets/fs2_water_storage.htm) — New York homeowner storage guidance; 6-inch casing approximation and storage table are not national requirements.
- [Maine CDC — Section 407.0 Recommended Minimum Recovery Rates](https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/SECTION-407-Recovery-Rates.pdf) — Maine Well Drillers and Pump Installers Rules recommendation; presented only as a regional example, not a national benchmark.
- [Connecticut Department of Public Health — Publication No. 28: Private Well Guidance for Determining Well Safe Yield](https://portal.ct.gov/dph/-/media/departments-and-agencies/dph/dph/environmental_health/private_wells/28privatewellguidancefordeterminingwellsafeyieldpdf.pdf?hash=002EC717EB075442072922C7F6AC95C4&rev=b07c25d4dc3c4e879a8b6ef4ad9c002d) — Connecticut private-well guidance; professional meter-testing example and state/local variation are not a national test prescription.
- [Connecticut Department of Public Health — Publication No. 28: Private Well Guidance for Determining Well Safe Yield](https://portal.ct.gov/dph/-/media/departments-and-agencies/dph/dph/environmental_health/private_wells/28privatewellguidancefordeterminingwellsafeyieldpdf.pdf?hash=002EC717EB075442072922C7F6AC95C4&rev=b07c25d4dc3c4e879a8b6ef4ad9c002d) — Connecticut private-well guidance; used to keep pressure-tank drawdown separate from aquifer recovery and to frame storage discussions.
- [Maine CDC — Private Well Water](https://www.maine.gov/dhhs/mecdc/healthy-living/health-and-safety/drinking-water-safety/private-well-water) — Maine private-well water-quality guidance; included for the post-event water-safety handoff, not as a recovery-rate rule.
- [Occupational Safety and Health Administration — 1910.333 Selection and Use of Work Practices](https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.333) — U.S. workplace electrical-safety regulation; the article does not claim OSHA directly regulates a homeowner's private well work.
- [Massachusetts Department of Environmental Protection — Private Well Guidelines](https://www.mass.gov/doc/private-well-guidelines/download) — MassDEP water-quantity table used as the primary reference for the worksheet's explicitly labeled geometric conversion; actual inside diameter and a uniform measured casing segment are required, and the conversion does not establish aquifer inflow or sustainable yield.
- [Massachusetts Department of Environmental Protection — Model Board of Health Regulations for Private Wells](https://www.mass.gov/doc/model-board-of-health-regulations-for-private-wells/download) — Massachusetts model regulation and local Board of Health guidance; used to support the article's record-audit checklist, not as a nationwide mandatory homeowner form.
- [Massachusetts Department of Environmental Protection — Estimating Private Well Yields using DEM's Well](https://www.mass.gov/doc/estimating-private-well-yields-0/download) — Massachusetts explanatory guidance; used to state the casing-storage assumption and comparability warning, not as a universal casing size, yield rule, or homeowner test prescription.
- [Massachusetts Department of Environmental Protection — Estimating Private Well Yields using DEM's Well](https://www.mass.gov/doc/estimating-private-well-yields-0/download) — Massachusetts explanatory guidance quoting an older Private Well Guidelines rule of thumb; not a national benchmark and not a substitute for the applicable local criterion or controlled professional evaluation.