Procedures for Flow Testing Hydrants

© 2001 Capt. Willis Lamm, Water Supply Officer, Moraga-Orinda (CA) Fire District

Part Two


In order to have valuable flow test data, readings need to be taken accurately and all necessary data collected. Gauges are checked regularly and recalibrated as necessary. Preprinted flow test forms are used which include places for the following information:

  • Location

  • Date

  • Time

  • Hydrant inventory No.

  • Hydrant Model

  • Water main size
  • Static reading at hydrant

  • Static reading on main

  • Residual reading on hydrant

  • Residual reading on main

  • Pitot reading

  • Name of tester(s)

At the hydrant.

Static, residual and pitot readings are necessary in order to determine the hydrant's total available fire flow beyond just what the one test outlet is flowing. The Hazen-Williams formula allows us to calculate this information based on the readings taken during our single outlet discharge. This formula allows us to accurately calculate what an engine could pump from the hydrant from multiple outlets and/or the large diameter pumper outlet.

On the water main.

Secondary static and residual readings taken somewhere close by on the same water main is important in order to take a look at how the main itself is performing and to calculate the reserve capacity of the main. This separate look is important since flow to the specific hydrant being tested may be limited by the capacity of the lateral serving the hydrant and the efficiency of the hydrant's design.

Date and time are important since there may be temporary heavy usage of the water system, reservoirs may be at unusual levels or pumping systems may be in operation. By recording dates and times, it can be determined if these or other factors caused unusual readings during the test.


Different reference sources offer different examples of recommended readings to be taken when flow testing of hydrants. Our testing standards are based on the following objectives:

  1. We need to have accurate data that tells us how much water is available from each hydrant in order to employ appropriate fire suppression tactics. (We may need to utilize all available water but not place more or larger fire streams than the hydrant can supply.)

  2. We need to have accurate data that tells us how much water is available from the grid in the event of a major fire that would require use of multiple hydrants. (Can the grid support multiple hydrants flowing or will opening a second or third hydrant grossly impact the flow from the hydrant(s) already flowing?)

  3. We need data that will allow us to determine if a weak hydrant is the result of an obsolete or degraded hydrant installation or mechanical problem, or whether the water main itself is performing poorly. (This data is also important in locating choked valves or other correctable factors that may be causing poor flow from a specific hydrant on a documented strong main.

  4. We need data that ISO will accept when evaluating our water supply system. (Water supply comprises 40% of a community's overall fire protection score.)

  5. We need data that is useful to water agency engineers in planning water system upgrade needs, capacity for expansion, identification of weak distribution areas, etc.

    By measuring static, residual and pitot at the hydrant being flowed we get the most accurate look at that hydrant's individual characteristics and efficiency. We can calculate pretty closely what that hydrant can provide when pumped down by a fire engine.

    By measuring static and residual from a nearby location, such as a fire hydrant adjacent to the hydrant being tested, or from a nearby residential water service, we can take an independent look at the water main itself and estimate its capacity with reasonable accuracy. Since flow from the hydrant is affected by friction loss in the lateral, street valve and the hydrant bury, we need to take additional readings from a "quiet" location where we can look at what is happening in the water main without such friction losses.

    The adjacent hydrant used to take secondary readings should not itself be flowing, but merely have a cap gauge attached so that readings can be taken.

    If the secondary reading is taken from a domestic line as opposed to an adjacent fire hydrant, the domestic user should not draw water during the few seconds that the test takes place to eliminate any chance of friction loss in the domestic service line skewing the readings taken there.

    Regardless as to where secondary readings are measured, static readings should be recorded prior to any water flowing and residual readings recorded with the test hydrant valve fully opened and water main pressure stabilized.

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