Water Supply Runtime Calculator
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The Redundant Water System Runtime Calculator calculates how many days a redundant water system can support its critical loads during a water outage. This information is an input for characterizing redundant systems in the TRN risk assessment methodology as part of Baseline Development (BD) Action 3. The calculator can account for three types of systems:

  • Onsite storage tank(s) connected only to the primary water supply,
  • Onsite or offsite secondary water source that supplies onsite storage tank(s),
  • Onsite or offsite secondary water source that directly supplies critical load(s),

After providing answers to the questions below, you will obtain an output estimating the number of days current redundant systems will be able to meet critical loads. This analysis provides a high-level estimate. For users who have done or are planning to do more refined assessments of the runtime capabilities for their redundant systems, those estimates may be more appropriate to use as inputs for the TRN analysis. Note that if your system is more complex than one of the system types listed above, it may require a more involved analysis to estimate system runtime. Review the system definitions to check to see if your system meets the criteria of analysis for this tool.

To see the calculations behind the results, click the “Show Calculations” checkbox. Click “Example” to see an example analysis including entered data and results.

Calculator related questions, suggests, and issues can be submitted here:

Type of redundant water system
Average daily water load for the system during an outage
gallons/day
Average daily water load for the system during an outage
gallons per minute
ERROR: Average daily water load must be greater than 0 gallons/day.
WARNING: The average daily water load you entered is larger than is typical, please confirm before proceeding.
Onsite Storage Tank

Enter the data below to characterize your onsite storage tank. Refer to the schematic water tank and the tool tips next to each question for more information.

Tank Storage Diagram
Useable tank volume
gallons
ERROR: Usable tank volume must be greater than 0 gallons.
WARNING: The useable tank volume you entered is larger than is typical, please confirm before proceeding.
Empty tank volume at any given point in time pre-outage
gallons
ERROR: Empty tank volume must be greater than 0 gallons and less than the useable tank volume.
Water loss factor for the piping between the storage tank and the load(s)
Secondary Water Sources

Enter the data below to characterize the water available from your secondary water source. Refer to the tool tips next to each question for more information.

Flow rate that can be provided by the onsite or offsite secondary water source supply
gallons/minute
ERROR: Flow rate must be greater than 0 gallons.
WARNING: The flow rate you entered is larger than is typical, please confirm before proceeding.
Water loss factor for the piping between the onsite or offsite secondary water source and the onsite storage tank (if present) or the load(s) (if no storage tank)
Usable secondary flow rate
gallons per minute
Set peak water load estimation type
Peak water load for the system during an outage
gallons/minute
ERROR: Peak water load must be greater than 0 gallons/minute.
WARNING: The peak water load you entered is larger than is typical, please confirm before proceeding.
Peak water load for the system during an outage
gallons per minute
Results

The results below show the calculated runtime for the redundant system described by the inputs to this calculator. The runtime is shown in days and in hours. Use the runtime in hours as an input to characterize your water redundant system in the TRN Baseline Development Action 3.

Complete the form and address any errors above to view calculated redundant water system runtime.
Longest duration of outage this redundant system could support
days The expected runtime is longer than the greatest outage modeled in the TRN. The expected runtime is zero days because the secondary supply is not sufficient to meet the peak load.
Input for 'Estimated Run Time (hrs)' in the TRN, Baseline Development Action 3
4,500 0 hours