Fire Hydrant Flow Testing & Fire Protection Plan Engineering

Fire hydrant flow testing is a standardized field procedure — governed by NFPA 291 (Recommended Practice for Fire Flow Testing and Marking of Hydrants) — that measures the actual water pressure and flow rate available at a specific fire hydrant location on the public water distribution system. The procedure measures three values:

• Static pressure (psi): The water pressure in the distribution main with no hydrant flowing — the baseline system pressure before any demand is placed on the system
• Residual pressure (psi): The pressure remaining at the test hydrant while a nearby flow hydrant is fully open and discharging — reflecting how much pressure the distribution system can maintain under fire flow demand conditions
• Flow rate (GPM): The volume of water discharged from the flow hydrant per minute — calculated using pitot gauge pressure and the outlet’s discharge coefficient

These three values are used together to calculate the available fire flow at a standardized residual pressure of 20 psi — the minimum system pressure that must be maintained during a fire suppression event per the International Fire Code and Texas Fire Code. This available fire flow (in GPM at 20 psi residual) is then compared against the required fire flow for the proposed building’s occupancy type and area to determine whether the existing water distribution system can support the development’s fire protection needs.

The flow test is not simply an administrative hurdle — it is the engineering measurement that determines whether an entire development can proceed as proposed, or whether water system improvements must be designed and constructed before a permit can be issued.

In San Antonio, fire hydrant flow tests are required by the San Antonio Fire Department (SAFD) and the City’s Development Services Department as a condition of building permit approval for a broad range of commercial and residential development. Common triggers include:

• New commercial construction of any occupancy type — retail, office, restaurant, medical, industrial, warehouse
• Multifamily residential development of 4 or more dwelling units — apartment complexes, condominiums, senior living facilities
• Industrial and warehouse facilities — particularly those with high-piled storage, flammable materials, or hazardous occupancy classifications that require higher fire flow
• Any occupancy requiring an automatic fire sprinkler system — the flow test provides the water supply data the sprinkler engineer must use as the design basis
• Building additions or changes of occupancy that increase the required fire flow above what the current installation was designed for
• SAWS water service upgrades — new or upgraded water meter connections that trigger a utility review of fire protection adequacy
• Insurance and ISO rating verification — property owners seeking to document fire protection adequacy for premium reduction or coverage purposes

When in doubt about whether your project triggers the SAFD flow test requirement, the correct answer is almost always to perform the test before permit submittal — not after. Discovering inadequate fire flow after a permit application has been filed, reviewed, and conditioned delays the project far more than a proactive pre-application test would have.

GGE recommends commissioning the fire hydrant flow test during the design development phase — before construction documents are completed — so that any water system deficiencies can be incorporated into the permit drawings rather than discovered during the permit review process.

A fire hydrant flow test is a field measurement — it produces three numbers (static pressure, residual pressure, and flow rate) that describe what is available in the water distribution system at the time and location of the test.

A fire protection plan is the engineering document that uses those numbers — along with the proposed development’s characteristics — to make the regulatory determination of whether fire protection is adequate and to specify what is required. Specifically, the fire protection plan:

• Identifies the building occupancy type, construction class, and building area
• Calculates the required fire flow in GPM per IFC Appendix B methodology
• Compares required fire flow to available fire flow from the hydrant test, at the code reference pressure of 20 psi residual
• Specifies required hydrant locations and maximum spacing to ensure complete building coverage within code-required hose-lay distance
• Establishes the water supply parameters (static and residual pressure, available flow) that the fire sprinkler engineer must use as the design basis for the automatic suppression system
• Identifies any water system improvements required before the permit can be approved

In Texas, a fire protection plan prepared for SAFD and building permit submission must be prepared and sealed by a Texas Licensed Professional Engineer. A sprinkler contractor, a building owner, or a non-engineering consultant cannot prepare this document legally.

GGE performs both the flow test and the fire protection plan as a single integrated engagement — the engineer who measures the water supply designs the protection plan that uses it. This eliminates the coordination gap that occurs when separate firms handle each phase.

The Insurance Services Office (ISO) assigns a Public Protection Classification (PPC) rating from 1 to 10 to communities throughout the United States — with Class 1 representing the best fire protection and Class 10 representing no recognized protection. The PPC rating is one of the primary factors that insurance underwriters use to calculate commercial and residential property insurance premiums. The three components of the ISO PPC scoring are:

• Fire department (50% of score): Equipment, staffing, training, and response time
• Water supply (40% of score): Available fire flow at hydrants throughout the community — measured using NFPA 291 flow test data
• Emergency communications (10% of score): Dispatch capabilities and communication systems

Because water supply represents 40% of the PPC score, fire hydrant flow test data has a direct and quantifiable impact on a community’s insurance classification — and on the individual property insurance premiums of every building within it. For commercial property owners, a single PPC rating improvement can reduce annual insurance premiums by a meaningful percentage on properties insured for millions of dollars.

Beyond community-level PPC ratings, individual property owners can commission GGE to perform flow tests specifically to document fire protection adequacy for insurance underwriting purposes — providing the PE-signed engineering report that underwriters require when evaluating risk on large commercial, industrial, or multifamily properties.

For commercial and industrial property owners in San Antonio whose buildings are insured based on fire protection adequacy assessments, a GGE fire flow test and PE-signed report provides the independent engineering documentation that insurance underwriters, ISO inspectors, and lenders require — and that self-reported or contractor-prepared assessments cannot supply.

Most engineering firms that perform fire hydrant flow tests understand the NFPA 291 field procedure — how to set up the equipment, read the gauges, and record the data. What most cannot provide is a meaningful engineering interpretation of what those numbers mean in the context of how the water distribution system actually behaves under fire flow demand conditions. That distinction is where GGE is different.

Gustavo Gonzalez, P.E. served as Director of Water Operations for the City of Corpus Christi — managing 150 employees responsible for operating and maintaining a water supply, treatment, and distribution system that included two reservoirs with combined storage of 1 million acre-feet and a 150 MGD treatment plant supplying over 115,000 acre-feet annually to a population exceeding 500,000. His key disciplines included Water Supply Management, Treatment Plant Operations, Distribution Systems, and TCEQ Compliance.

That institutional knowledge translates directly into fire hydrant flow test practice in three ways:

• System behavior interpretation: Gonzalez understands the factors that cause flow test results to understate system capacity — main age, pipe diameter, system demand timing, and valve configurations — and evaluates results in that context rather than treating raw numbers as absolute
• SAWS coordination: Experience with water utility operations gives GGE an institutional understanding of what SAWS engineering staff require for flow test notification, improvement plan review, and utility connection approval
• Water main improvement design: When test results reveal inadequate fire flow, GGE’s civil engineering team designs the water main upgrades, hydrant installations, or on-site storage solutions required for compliance — with the same team that completed a $750,000+ water main replacement project for the ROC USA community infrastructure program in San Antonio

GGE’s fire hydrant flow testing is backed by the only thing that gives test results their full value: an engineer who has managed water distribution systems at scale, who understands what the numbers measure and what they don’t, and who can design the improvements when they reveal a deficiency.