# How to Read a Well Pump Curve for Depth and Pressure

Source: https://brictale.com/water/pumps/read-well-pump-curve
Published: 2026-08-22
Audience: Homeowner
Published by Brictale, a consumer home-intelligence publication. https://brictale.com

## Short answer

Read the curve as head versus flow, then build a datum-matched duty point: pumping water level + signed elevation to the pressure point + PSI × 2.31 + bidder-calculated friction. Plot it at the stated flow against the exact model curve, not a horsepower label. Missing datum, flow, TDH, friction calculation, or model curve means the quote is incomplete.

---

Start with the duty point, not the horsepower. A well-pump curve tells you how much head a specific pump can produce at a specific flow. Your quote is credible only when it shows the same two things for your system: the total dynamic head required and the flow you need at the pressure you want.

For a usable worksheet, choose one common discharge datum first—normally the pressure-gauge or tank connection used for the quote. Enter the pumping water level as a positive depth below that datum. Measure or state the desired pressure at that same datum. If the desired pressure is at another point, include its signed elevation relative to the datum and the friction between the datum and that point.

The homeowner worksheet is:

`total dynamic head (ft) = pumping water level below common datum (ft) + signed elevation to pressure point (ft) + pressure head (PSI × 2.31) + generalized system friction loss (ft)`

Use a positive elevation term when the pressure point is above the common datum, a negative term when it is below, and zero when the points share the datum. The expanded friction term is a generalized worksheet model, not a residential loss value established by the vertical-turbine source cited below. Require the bidder to replace it with a calculation for the actual residential pipe, fittings, valves, filters, and distribution segment before treating a duty point as supported.

Then plot the result at the stated flow on the exact manufacturer's curve. If the quote gives only “1 HP replacement” or “20 GPM pump,” it has not yet shown that the pump can meet your home's depth, pressure, elevation, and pipe losses. This page helps you identify the missing evidence and compare quotes; it does not select a pump, wire, control box, or installation method.

## Read the curve in one sentence

A conventional pump curve has flow on the horizontal axis and head on the vertical axis. Franklin Water's pump-testing guidance describes the same layout and recommends plotting measured points against the factory curve. [Franklin's explanation of pump-curve testing](https://www.franklinwater.com/resources/news/?newsItemID=18096) is written for vertical turbine pumps, so use it for the reading method, then use the exact residential pump documentation for the decision.

### What “head” means here

Head is the energy the pump must add to move water through the system. It is usually shown in feet of water, even though your pressure gauge reads PSI. One PSI is approximately 2.31 feet of water head under the ordinary-water assumption used in this worksheet. That conversion follows the [U.S. Geological Survey pressure conversion table](https://pubs.usgs.gov/twri/twri8a3/), which lists about 0.433 PSI per foot of water.

This is why a pressure request is not a separate alternative to depth. A request for 50 PSI represents about 115.5 feet of head before you count the lift from the well or friction in the pipe. The pump curve does not know that your gauge says “50”; it responds to the combined head requirement.

### What the curve does not tell you

The curve is not a universal horsepower chart. It is a performance statement for a model, pump stage or impeller configuration, speed, frequency, and sometimes a particular motor combination. A current [Goulds residential performance-curve document](https://www.xylem.com/siteassets/brand/goulds-water-technology/resources/brochure/gsspec.pdf) shows separate curves and recommended ranges for model families; the model name and curve are part of the evidence.

Do not move from “the curve reaches 300 feet” to “this pump is right for my well.” You still need to confirm:

- The curve is for the exact pump model or an explicitly compatible configuration.
- The plotted flow is the flow your well and home can support.
- The curve uses the same frequency and operating mode as the quote.
- The motor, control box or drive, voltage, cable, tank, check valves, and pipe are compatible.
- The well will not be over-pumped at the proposed duty point.

## Build your homeowner duty point

Your duty point is the pair `(flow, total dynamic head)`. It is a comparison input, not a pump-selection command. Record each component separately so a bidder can correct an assumption instead of hiding it in one impressive-looking number.

{{visual:duty-point-quote-check}}

| Input | Your value | How to obtain it | What it means |
|---|---:|---|---|
| Required flow | ___ GPM | Use a stated household peak or a professional flow test | The horizontal coordinate; do not substitute pump marketing capacity |
| Pumping water level | ___ ft below common discharge datum | Use a recent qualified measurement under a stated demand | The vertical lift component while water is being drawn |
| Desired pressure | ___ PSI | Record the intended pressure at that same datum, or identify another pressure point | Convert with PSI × 2.31 |
| Signed elevation term | ___ ft | Measure the pressure point relative to the common datum; use 0 when they match | Adds head for a point above the datum or subtracts it for a point below |
| Pressure head | ___ ft | Desired PSI × 2.31 | Pressure expressed in curve units |
| Generalized friction term | ___ ft | Use only as a clearly bounded provisional allowance; require the bidder's residential calculation before a verdict | A worksheet scope covering drop pipe, fittings, valves, filters, and distribution piping; it is not a sourced residential loss value |
| Total dynamic head | ___ ft | Water level + signed elevation + pressure head + bidder-calculated friction | The vertical coordinate to plot |

### Use pumping water level, not drilled depth

The drilled depth is a property of the well record. It does not tell you where the water surface sits while the pump is supplying water. The [EPA maintenance guide](https://www.epa.gov/sites/production/files/2015-04/documents/epa816b04002.pdf) distinguishes static water level, when the pump is off, from pumping water level, while water is being drawn. The second value is normally the one that belongs in this duty-point calculation.

Static level is still useful. It provides a baseline and can reveal change over time. But a quote that uses “the well is 400 feet deep” as though all 400 feet are lifting head may be using the wrong datum. Conversely, a quote that uses a shallow static level while the level falls sharply during demand may understate the lift.

Ask the bidder to write down:

- The common discharge datum and pressure point. If they differ, show the signed elevation term and any downstream friction instead of silently mixing reference points.
- Whether the level is static or pumping.
- The flow and duration associated with the pumping reading.
- The date, season, and whether other household demand was running.
- The source of the value: well record, prior test, or new measurement.

If pumping water level is unknown, mark it as unknown. Do not turn a guessed pump setting or drilled depth into a false measurement.

### Convert the pressure you actually want

Use the pressure at the common discharge datum whenever possible. If the quote promises a pressure at the tank gauge but your concern is a second-floor fixture, do not combine the tank-gauge PSI with a fixture-height water level as though they were one datum. Either ask the bidder to translate the desired fixture pressure back to the common datum or include the fixture's signed elevation and the friction from the datum to the fixture in the worksheet.

Example worksheet:

| Calculation | Example |
|---|---:|
| Common discharge datum | Pressure-tank gauge |
| Pumping water level below that datum | 180 ft |
| Desired pressure at that same datum | 50 PSI |
| Signed elevation term | 0 ft |
| Pressure head | 50 × 2.31 = 115.5 ft |
| Generalized friction allowance | 25 ft, clearly labeled as an assumption |
| Total dynamic head | 180 + 0 + 115.5 + 25 = 320.5 ft |
| Duty point | 10 GPM at approximately 321 ft TDH |

The 25-foot value in this example is not a recommendation, measurement, or residential friction value supported by the Franklin vertical-turbine article. It is an intentionally visible generalized worksheet allowance. A real quote must replace it with a residential calculation based on pipe diameter, length, fittings, valves, filters, the distribution segment, and the stated flow, with the method or source identified. If the installer cannot show those inputs, use an amber result; do not use the allowance to call the duty point green.

## Plot the point against the exact curve

Once you have a duty point, read the curve in this order.

### 1. Verify the document identity

Write down the manufacturer, product family, exact model, horsepower, voltage, phase, frequency, number of wires, stages or impeller configuration, and any controller or drive. Download or save the curve used in the quote. A screenshot with no model number is not enough.

Manufacturer manuals often separate hydraulic data from electrical data. In [Pentair's 4-inch submersible-pump manual](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf), motor tables identify voltage, horsepower, winding or running information, fusing, and cable guidance by model. That does not make those values interchangeable with another brand; it shows why the exact model matters.

### 2. Find the flow on the horizontal axis

Use the design flow stated by the quote. If you need to compare two bids, require both bidders to use the same flow. “This pump is rated 10 GPM” can mean a series label or a nominal performance class; it does not by itself establish 10 GPM at your required head.

If the household demand is uncertain, record the decision as a range instead of choosing one arbitrary number. For example, a professional may evaluate 8 GPM for ordinary simultaneous use and a higher case for irrigation. The point is to make the assumption visible and ask what the well can sustain.

### 3. Move up to the required head

At the chosen flow, find the curve's available head. If the curve is below your required TDH, the displayed pump cannot meet that duty point under the curve's stated conditions. If it is above the point, that is only a screening pass. The pump must still operate within the manufacturer's recommended range and the system must handle its pressure, flow, electrical load, and controls.

Do not read the leftmost shutoff point as usable household performance. A pump can show high head at nearly zero flow and still be a poor match for the home's required flow. A curve can also extend past a manufacturer's recommended range; use the documented range, not the most flattering edge of the graph.

### 4. Look for the operating point, not a single “maximum” number

The real system settles where the pump's available head matches the system's required head at a flow. A quote may show a pump curve but omit the system side of the comparison. Your worksheet supplies that missing side: lift, pressure, and friction at the same flow.

For a homeowner quote check, use these screening labels:

| Result | Evidence on the page or quote | Action |
|---|---|---|
| Green | Exact curve identified; common datum or signed elevation is explicit; bidder's residential friction calculation supports the duty point at the stated flow; range, well yield, electrical compatibility, and controls are addressed | Ask for the final written scope and commissioning readings |
| Amber | Curve is present but pumping level, friction calculation, flow, pressure datum, or elevation term is estimated or missing | Ask for the missing measurement or a clearly bounded bidder calculation before approving |
| Red | Horsepower-only recommendation; no exact curve; duty point falls outside the curve; or low-yield/electrical/pressure limits are unresolved | Pause the comparison and request qualified design review |

“Green” means the hydraulic comparison is documented. It is not a warranty that the pump will perform as promised, and it does not authorize homeowner installation.

## Check the quote for the hidden system

A pump curve is only one part of the proposal. The quote should show how the rest of the water system will live with that pump.

### Well yield and drawdown

The pump cannot create water the aquifer does not supply. [Penn State Extension's guidance on low-yielding wells](https://extension.psu.edu/using-low-yielding-wells) explains that a normal pump may pull the water level down to a critical point faster than the well replenishes, and that a larger pressure tank alone does not fix the underlying yield problem.

Ask whether the proposed flow is:

- A measured or documented well yield.
- A short-term pump-test result.
- A household peak-demand assumption.
- A manufacturer model label.

Those are different facts. If the well's sustainable yield is lower than the home's peak demand, a professional may discuss demand management, a larger storage strategy, or intermediate storage. Penn State describes intermediate storage as a system in which the well supplies a limited rate to a reservoir while a separate pressure pump serves demand. That is a design option for a qualified professional to evaluate, not an automatic reason to add a tank.

### Pressure limits and protection

The requested PSI must be compatible with the tank, piping, controls, relief protection, fixtures, and the pump's shutoff behavior. [Pentair's manual](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf) warns that submersible pumps can develop very high pressure, says not to operate with the discharge completely closed, and specifies product-specific relief-valve capacities for different tank arrangements.

Do not copy those relief-valve numbers into a different installation as though they were a national code rule. Instead, ask the bidder to identify the applicable manufacturer's instruction, local code or inspection requirement, tank arrangement, relief-valve location, and full-flow capacity. The quote should explain what prevents the pump from running against a closed discharge or exceeding a component rating.

### Electrical and control compatibility

Horsepower is not enough to select a motor circuit. The proposal should identify voltage, phase, frequency, motor wiring, control box or drive, cable size and length, disconnecting means, grounding or bonding, and protection. [Pentair's troubleshooting tables](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf) connect low or high running voltage, a mismatched control box, undersized wire, and cable faults with motor problems, and direct electrical faults to qualified personnel.

For a replacement quote, ask whether the existing wiring and controls were tested or simply assumed reusable. If the answer is “same horsepower,” the quote is missing the compatibility check. If a variable-speed drive is proposed, ask for the motor and drive models, pressure setpoint, sensor, minimum-flow behavior, tank requirement, surge protection, and fault response.

### Pump setting and drop pipe

The pump's setting depth is not the same as the pumping water level. It is an installation choice constrained by water level, well bottom, pump cooling, pipe, cable, and manufacturer instructions. In [Pentair's PN280 manual](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf), the specified products are to sit 15 to 20 feet below the lowest pumping level and at least 5 feet above the bottom. Treat this as a model-specific example, not a universal homeowner rule.

Require the quote to state the proposed setting depth and what evidence supports it. If the bidder proposes lowering the pump because the water level falls, ask how the new position stays above the bottom and away from sediment, and how the pipe, cable, well diameter, motor cooling, and recovery rate remain acceptable.

## Make safe measurements before you compare

The purpose of homeowner measurement is to improve the question for a professional, not to turn the homeowner into a pump technician.

### Safe homeowner observation checklist

Do these only from accessible, normal-use points. Stop if water is unsafe to discharge, the gauge is damaged, the wellhead is inaccessible, or any step would require removing a cover.

- Photograph the pump, motor, control box, pressure tank, gauge, and switch labels without opening energized equipment.
- Record the pressure gauge reading with no intentional water use, then during one ordinary fixture flow if the gauge can be observed safely.
- Measure a safe, accessible outlet by collecting a known volume and timing it. `GPM = gallons collected ÷ seconds × 60`. Label the outlet, faucet opening, and whether other fixtures were running. This is an observation of that outlet, not proof of pump capacity or well yield.
- Note pressure drop, air, sediment, cycling, or a pump that runs continuously. Treat these as symptoms, not diagnoses.
- Gather the well completion record, pump invoice, prior water-level readings, service history, and any prior flow test.
- Ask every bidder to return the same worksheet with their assumptions marked measured, documented, or estimated.

Do not open a pressure switch, control box, disconnect, junction box, or other energized control. Do not test live wiring. Do not open the well seal, remove the well cap, drop a tape or probe into the well, pull the pump, enter a pit or confined space, or manipulate pressurized equipment. Do not run the pump against a closed valve. Pentair's manual identifies hazardous voltage, grounding requirements, hazardous pressure, and pump-disassembly hazards; electrical, well-opening, retrieval, pressure, and commissioning work belongs to qualified professionals.

### What requires a professional reading

The most valuable missing field is often pumping water level under a known flow. A professional can choose an appropriate method and account for the equipment already installed. The same is true for electrical current, insulation, winding, control, well-yield, and system-pressure tests. Do not infer a failed pump from low pressure alone; a low water level, clogged filter, check valve, pipe leak, control fault, tank issue, wiring problem, or well condition may produce a similar symptom.

The safest next step when a quote is vague is not to buy a larger pump. Ask: “What measurement would change your recommendation?” A sound bidder should be able to name the missing value and explain how it affects the duty point.

## Use failure branches to challenge a recommendation

The same pump curve can appear to solve different symptoms, but the cause may be elsewhere. Use this matrix to keep the quote conversation diagnostic.

| What you observe | What it may mean | What the curve can and cannot answer | Next safe step |
|---|---|---|---|
| Low pressure at fixtures | Pump mismatch, low water level, restriction, filter, tank or control issue | Can test whether the proposed pump supports a documented duty point; cannot diagnose the cause alone | Request pressure and flow observations plus professional system diagnosis |
| Pump runs continuously | Demand exceeds supply, leak, low water, restriction, control or pump problem | Can show whether the pump can reach the required head at flow; cannot prove why it never reaches shutoff | Avoid repeated cycling or live tests; ask for a written diagnostic plan |
| Pressure falls after several minutes | Drawdown or well-yield problem is possible | A curve does not establish aquifer yield | Request pumping-level and recovery information from a qualified professional |
| Breaker or overload trips | Voltage, cable, control, motor, or mechanical issue | Horsepower label is not enough to check electrical compatibility | Keep covers closed and have qualified electrical/pump service test it |
| Air, sand, or cloudy water | Well, water-quality, piping, or pump condition issue | A curve cannot evaluate water quality, contamination, potability, or solids tolerance | Do not drink, cook with, make ice from, or brush teeth with suspect water; avoid other exposure as appropriate, obtain qualified drinking-water testing, and follow local health guidance before treating it as potable |
| Quote says “upgrade to 1.5 HP” | A generic capacity recommendation | No curve, flow, head, or compatibility evidence | Ask for exact model, duty point, curve, controls, and protection |

### Treat a horsepower-only quote as unsupported

Horsepower is an input to a pump package, not the homeowner's result. Different pumps with the same horsepower can have different head-flow curves. A higher horsepower pump can also be a poor answer if the well yield is low, the pressure tank and controls are not compatible, the cable is undersized, or the system is not designed for the added flow.

Water appearance is a separate safety question. A pump curve can describe hydraulic performance; it cannot establish potability or diagnose contamination. The [EPA's private-well testing guidance](https://www.epa.gov/privatewells/protect-your-homes-water) advises prompt testing after a change in odor, color, or taste and recommends a certified drinking-water laboratory. The [CDC's well-water testing guidance](https://www.cdc.gov/drinking-water/safety/guidelines-for-testing-well-water.html) likewise puts responsibility for checking private-well drinking water on the owner. Visual symptoms do not prove that water is unsafe or safe, so if contamination is suspected, stop drinking or using the water for food and other potentially harmful exposure as appropriate, and obtain qualified testing and health guidance before treating it as potable.

Ask the contractor to revise “replace with 1 HP” into a statement like: “At ___ GPM and ___ feet TDH, model ___ on curve ___ is expected to meet the stated duty point; pumping level measured on ___; friction calculated from ___; voltage/control/cable verified by ___.” The wording is not a guarantee. It is a testable record.

## Finish with a documented decision and commissioning record

Before approval, make a one-page comparison with the same columns for every bidder:

1. Exact pump, motor, voltage, phase, frequency, stages or configuration.
2. Design flow and where that flow is measured or assumed.
3. Static and pumping water levels, datum, date, and test condition.
4. Desired pressure and gauge location.
5. Friction calculation inputs and total dynamic head.
6. Curve document, revision, and plotted duty point.
7. Well-yield or recovery evidence and any low-water protection.
8. Drop pipe, cable, splices, check valves, controls, tank, gauge, relief protection, and wellhead scope.
9. Electrical, permit, inspection, disinfection, flushing, testing, disposal, and restoration assumptions.
10. Warranty boundary: parts, labor, removal, shipping, reinstallation, and return visits.

After installation, the professional should record the installed model and settings, operating pressure and flow at a stated condition, voltage and current readings, control operation, leak check, and any water-level or well-yield test used in the design. Preserve the curve and the final worksheet with the property records. The [Franklin AIM resource page](https://www.franklinwater.com/resources/franklin-aim) currently lists a 2026 manual and installation-record forms; a manufacturer's installation record is useful because it preserves the model and operating context for the next service call.

Do not treat the final reading as a homeowner electrical test. Ask the installer to supply the record and explain any result that differs from the quote.

### The decision in plain language

Choose the quote that makes the duty point auditable: a stated flow, a measured or bounded pumping water level, a visible pressure conversion, a friction calculation, and an exact model curve. Then require evidence that the well can supply that flow and that the motor, controls, wire, tank, relief protection, pipe, and local installation requirements match.

If any of those pieces are missing, the honest output is “not enough evidence yet,” not “buy more horsepower.”

This worksheet is a comparison aid. It is not a diagnosis, engineering design, local-code interpretation, pump-selection authorization, or promise of performance. Never open energized controls, test live wiring, open a well, pull a pump, enter a confined space, or manipulate pressurized equipment as part of this comparison; use a qualified well or electrical professional for those tasks.

## Evidence

- [Franklin Water — Franklin AIM (2026 AIM Manual)](https://www.franklinwater.com/resources/franklin-aim) — Franklin Electric resource page; 60 Hz English submersible-motor guidance. The existence of the manual does not establish suitability for a specific residential installation.
- [Franklin Water — Troubleshooting Vertical Turbine Pumps](https://www.franklinwater.com/resources/news/?newsItemID=18096) — Manufacturer educational guidance for vertical turbine pump testing. It does not establish residential losses for drop pipe, fittings, valves, filters, or distribution piping; the article labels that broader friction term as a generalized worksheet model and requires the bidder's residential calculation before a quote verdict.
- [Franklin Water — Troubleshooting Vertical Turbine Pumps](https://www.franklinwater.com/resources/news/?newsItemID=18096) — Manufacturer educational guidance for vertical turbine pump testing; an explanation of curve reading, not a performance claim for an unspecified residential model.
- [Pentair — 4-Inch Submersible Pumps Manual (PN280)](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf) — Pentair 4-inch submersible pump families covered by PN280. These distances are manufacturer-specific and are not a universal rule for every well pump.
- [Pentair — 4-Inch Submersible Pumps Manual (PN280)](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf) — Pentair installation and troubleshooting safety instructions; local electrical requirements and the installed equipment govern the work.
- [Pentair — 4-Inch Submersible Pumps Manual (PN280)](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf) — Pentair 4-inch submersible pump installation instructions. The pressure-relief values are product-specific instructions, not a national code summary.
- [Penn State Extension — Using Low-Yielding Wells](https://extension.psu.edu/using-low-yielding-wells) — Penn State Extension guidance for low-yielding wells; system design, well yield, and storage choices must be evaluated for the specific property.
- [U.S. EPA — Preventive Maintenance Tasks for Tribal Drinking Water Systems Guide Booklet](https://www.epa.gov/sites/production/files/2015-04/documents/epa816b04002.pdf) — EPA guide for tribal drinking-water systems; use the definitions and recordkeeping concept as reference, not as a private-well regulatory requirement.
- [U.S. Geological Survey — Use of Submersible Pressure Transducers in Water-Resources Investigations](https://pubs.usgs.gov/twri/twri8a3/) — USGS hydrologic conversion reference. Actual pressure-head conversion can vary with fluid density and temperature; this worksheet assumes ordinary household water.
- [Xylem / Goulds Water Technology — GSSPEC R4 Performance Curves (2025)](https://www.xylem.com/siteassets/brand/goulds-water-technology/resources/brochure/gsspec.pdf) — Goulds residential 60 Hz performance-curve document, revision R4 dated 7/2025. The curves apply only to the listed pump models and conditions.
- [Pentair — 4-Inch Submersible Pumps Manual (PN280)](https://www.pentair.com/content/dam/extranet/web/nam/pentair/manuals/pn280-4inch-submersible-pumps-iom.pdf) — Pentair troubleshooting tables and cable guidance for covered motors. Do not use these values to size another manufacturer's installation.
- [Penn State Extension — Using Low-Yielding Wells](https://extension.psu.edu/using-low-yielding-wells) — Penn State Extension design discussion for low-yielding wells; it is an option to evaluate with a qualified well professional, not a universal retrofit recommendation.
- [U.S. EPA — Protect Your Home's Water](https://www.epa.gov/privatewells/protect-your-homes-water) — EPA private-well guidance; the article uses it to set a non-diagnostic boundary. A pump curve is not a water-quality test, and local health-department advice governs an actual suspected-contamination event.
- [CDC — Guidelines for Testing Well Water](https://www.cdc.gov/drinking-water/safety/guidelines-for-testing-well-water.html) — CDC consumer guidance for private drinking-water wells; it supports testing and health guidance, not pump sizing or a determination that a particular sample is potable.