How to Fill Out and Submit a Fire Hydrant Flow Test Form

A fire hydrant flow test form records the water pressure and flow available at a specific point in the municipal system, and you complete it in the field by capturing three readings during a controlled test: static pressure, residual pressure, and pitot (velocity) pressure. Most reviewers accept the layout in NFPA 291, though your water utility or fire marshal may hand you a local template that asks for the same core data. Fill every field, use calibrated gauges, run the test between at least two hydrants, and have it certified by someone your jurisdiction recognizes. Incomplete or improperly conducted tests get sent back, and a certificate of occupancy will not issue until an accepted form is on file.

When a Flow Test Form Is Required

New construction is the usual trigger. Before a fire marshal approves building permits, the sprinkler designer needs certified flow data to size the system, and NFPA 13 requires water supply information for hydraulic calculations that comes directly from a completed flow test form.¹ Renovations and changes in occupancy also call for a fresh test, because old data no longer reflects what the building needs.

If the property has private hydrants, NFPA 25 sets a separate maintenance rhythm: annual visual and operational checks, with a full pitot flow test every five years. That testing uses the same form and the same technique described below, but it is a recurring compliance exercise rather than a one-time permit document.

Equipment to Bring to the Field

You cannot produce a valid form from a single hydrant. The test requires at least two: one as the static/residual hydrant where you read pressure, and one or more flow hydrants where water discharges.² Position the static/residual hydrant between the flow hydrant and the main that supplies the area.

A 200 psi pressure gauge that threads onto the 2½-inch outlet of the residual hydrant, with an air relief valve.
A pitot gauge to read velocity pressure in the discharge stream, or a diffuser with a built-in pitot.
A hydrant wrench.
Calipers or a tape measure to record the inside diameter of each discharge orifice.

Calibrate every pressure gauge before you go out. Annual recalibration is the floor, and heavy field use shortens that interval.³ Uncalibrated gauges are among the most frequently cited pitfalls in hydrant testing and can throw off the whole calculation that lands on the form.⁴ Digital pressure loggers are gaining acceptance as a supplement, but confirm with your authority having jurisdiction (AHJ) first; some still require a manual pitot reading as the official record.⁵

Running the Test to Get Valid Numbers

NFPA 291 recommends testing during peak demand hours, since street pressures can swing by 10 psi or more between early morning and midday.⁶ Reviewers look at the time of day on the form to judge whether conditions were realistic. Inspect both hydrants for damage or leaks before opening anything, and confirm nearby storm drains are clear.

Static Pressure

Remove the 2½-inch cap on the residual hydrant and thread on the pressure gauge with the air relief valve open. Open the hydrant valve fully, let water bleed from the relief valve, then close it. Give the needle a minute to settle. That reading is the static pressure, taken with no water flowing from any test hydrant, and goes on the form.

Residual and Pitot Pressures

At the flow hydrant, remove the caps on the ports you plan to flow and open the valve fully. Let it run long enough to flush debris. While water is discharging, take two simultaneous readings:

Pitot pressure, read in the center of the discharge stream about half an orifice diameter from the opening. A diffuser with a built-in gauge handles the positioning for you.
Residual pressure, read at the gauge on the first hydrant while the flow hydrant is still running.

Record how many minutes the hydrant flowed and note the hydrant butt type (smooth and rounded, square-edged, or projecting inward), because the butt determines the discharge coefficient. Close the flow hydrant slowly to avoid water hammer.

Confirm the Pressure Drop

Compare static to residual. You need at least a 10 percent drop for the data to be reliable. If the drop is smaller, the flow hydrant did not stress the system enough. Open additional ports or flow a second hydrant and repeat before you commit numbers to the form.²

Fields on the Form

Whether you use the NFPA 291 layout or a local version, the same core data has to appear, and an incomplete worksheet is itself grounds for rejection.⁷⁴

Location: nearest intersection or address, plus the unique ID stamped or painted on each hydrant used.
Date and time of the test.
Static pressure in psi.
Residual pressure in psi.
Pitot pressure in psi.
Orifice diameter in inches, measured with calipers at each flowing outlet.
Hydrant butt type: smooth and rounded, square-edged, or projecting inward.
Coefficient of discharge (C): 0.90 for smooth and rounded, 0.80 for square-edged, 0.70 for projecting inward.⁸
Elevation differential between the residual hydrant and the flow hydrant. Omitting this is a common pitfall.⁴
Flow duration in minutes.

Calculating Flow for the Form

Convert pitot pressure to a flow rate using:

Q = 29.83 × C × d² × √P

Q is flow in gallons per minute, C is the coefficient of discharge, d is the orifice diameter in inches, and P is the pitot pressure in psi.⁸ Picking the wrong coefficient is one of the most common calculation errors. A smooth-bore outlet at 0.90 produces a flow nearly 30 percent higher than a projecting outlet at 0.70 for the same pitot reading, so verify the butt type before plugging in the number.² Fire flow is formally defined as the flow available at 20 psi residual pressure, which is what the engineer will extract from your numbers downstream.⁹

Mistakes That Get the Form Rejected

Running the test from a single hydrant. You need two: one for pressure, one for flow.²
Placing the residual hydrant on the wrong side of the flow hydrant relative to the main.
Reporting a static-to-residual drop under 10 percent.
Entering a coefficient that does not match the butt type on the hydrant you flowed.
Using gauges that were not calibrated before the test.⁴
Leaving the elevation differential blank when the two hydrants sit at different heights.
Blank fields anywhere else on the worksheet, including flow duration and butt type.

Who Is Allowed to Certify the Form

Jurisdictions decide who can sign. Some accept licensed fire protection engineers or licensed fire protection contractors. Others require the local fire agency or water district to perform or witness the test. California, for example, limits certification to the responsible fire agency, the local water district, a licensed C-16 fire protection contractor, or a licensed fire protection engineer, and whoever certifies the result must have witnessed the test.¹⁰ A water authority representative often attends to confirm the readings and to make sure the setup does not create a cross-connection that could contaminate the potable supply. When the hydrant feeds temporary construction water, many jurisdictions also require a tested backflow preventer. Submitting a form signed by someone outside the approved list means automatic rejection.

Submitting the Completed Form

Most municipalities take the completed form through a digital permit portal alongside the building plans; some still want a hard copy delivered to the fire marshal’s office. Either way, submit it before requesting plan review for the fire suppression system. The sprinkler designer cannot finalize hydraulic calculations without the test data, and the fire marshal will not review an incomplete plan set.

Turnaround varies by jurisdiction. Some water utilities return results within ten business days of receiving payment and the request, subject to weather and crew availability.¹¹ Others take longer. You will receive either a notice of acceptance or a request for clarification, usually a retest tied to one of the errors listed above. Build that lead time into the project schedule, because the certificate of occupancy will not issue until the fire marshal has an accepted flow test on file. Insurance carriers may ask for a copy as well, particularly on commercial projects where the suppression system directly affects premiums.

1
National Fire Protection Association. Calculating the Required Fire Flow
2
WSRB. Guide to Hydrant Flow Testing
3
Mid-West Instrument. How Often Should I Check the Calibration of My Pressure Gauge?
4
MWUA. NFPA 291 Hydrant Flow Testing
5
YSI. PL200-H Hydrant Water Pressure Logger
6
QRFS. NFPA Guidance on Fire Hydrant Testing
7
National Fire Protection Association. NFPA 291 – Recommended Practice for Water Flow Testing and Marking of Hydrants
8
South Salt Lake City. Water Based Fire Protection and Water Supply Systems
9
National Fire Protection Association. Fire Hydrants and Water Flow
10
California Legislative Information. California Code of Regulations Title 25 Section 2317 – Private Fire Hydrant Test and Certification
11
WaterOne. Fire Hydrant Flow Testing