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Water Tower Storage Calculator - Fire Flow, Peak Demand & Emergency Reserve Sizing

Size elevated storage for small water systems using AWWA guidelines

Free water tower and elevated storage sizing calculator. Enter average daily demand, fire flow requirements, and emergency reserve needs to get total required storage volume with a breakdown by purpose. Follows AWWA standards with recommendations for standard tank sizes. Calculate from population or known demand, with peak hour demand factoring and fire suppression duration.

Pro Tip: Fire flow storage dominates the calculation for most small systems. A 1,500 GPM fire flow for 2 hours requires 180,000 gallons - which alone exceeds many small towns' entire average daily demand. Size for fire storage first, then check if peak demand and emergency reserve are already covered.

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Water Tower Storage Sizing Calculator
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How It Works

  1. Enter Average Daily Demand

    Input your system's average daily water demand in gallons per day, or calculate it from population served times per capita usage (typical: 80-150 GPD per person).

  2. Set Fire Flow Requirements

    Enter the required fire flow in GPM and duration in hours. Typical small-town values: 500-1500 GPM for 2 hours. Check with your local fire authority or ISO rating requirements.

  3. Set Peak Demand and Emergency Reserve

    Enter peak hour demand factor (typically 2.0-3.0 for small systems) and emergency reserve in days (typically 1 day for systems with backup supply).

  4. Review Sizing Results

    Get total required storage with a breakdown showing fire, peak, and emergency components. The calculator recommends the nearest standard tank size and shows any surplus or deficit from existing storage.

Built For

  • Small town water systems evaluating storage adequacy
  • Rural water districts planning storage expansion
  • Engineers sizing new elevated tanks for development projects
  • Water system operators comparing actual storage to AWWA guidelines
  • Grant applications requiring storage needs documentation

Frequently Asked Questions

Total required storage = fire suppression + peak demand equalization + emergency reserve. Fire storage = fire flow (GPM) × duration (hours) × 60 minutes. Peak equalization covers the gap between supply rate and peak demand. Emergency reserve is typically one day of average demand. For most small systems, fire storage is the largest component.
AWWA recommends that elevated storage equal the average daily demand for systems under 3,300 connections. For larger systems, storage should cover fire flow plus peak hour equalization. Many states have their own requirements that may be more or less strict than AWWA guidelines.
At 100 GPD per person, average demand is 100,000 GPD. Fire storage at 1,000 GPM for 2 hours adds 120,000 gallons. Emergency reserve adds another 100,000 gallons. Total: roughly 320,000 gallons minimum. A 300,000 or 500,000 gallon tank would be the standard size recommendation depending on local requirements.
Disclaimer: This calculator provides sizing estimates based on AWWA guidelines and standard engineering practice. Actual storage requirements depend on your state regulations, local fire authority requirements, system configuration, and supply reliability. Consult a licensed professional engineer for system design.

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