Water Distribution Calculator
Design water mains and distribution systems per AWWA
Demand Information
Fire Flow Requirements
Per ISO/IFC requirements
System Configuration
During fire flow (20 PSI typical)
+ for uphill, - for downhill
Distribution Requirements
Recommended Main Size
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Peak Demand + Fire Flow
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Average Daily Demand
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Peak Hour Demand
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Velocity (Peak + Fire)
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Headloss
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Residual Pressure
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System notes will appear here.
Water Demand Factors
| Use Type | Average GPD | Peak Factor |
|---|---|---|
| Single Family | 300-400 GPD/unit | 2.5-3.0 |
| Multi-Family | 200-250 GPD/unit | 2.0-2.5 |
| Apartment | 150-200 GPD/unit | 2.0-2.5 |
| Office | 0.1-0.2 GPD/sq ft | 2.0 |
| Retail | 0.1-0.15 GPD/sq ft | 1.5 |
| Restaurant | 50-100 GPD/seat | 2.5 |
| Hotel | 100-150 GPD/room | 2.0 |
Fire Flow Requirements (ISO)
| Construction Type | Area (sq ft) | Fire Flow (GPM) | Duration |
|---|---|---|---|
| 1-2 Family Dwelling | <3,600 | 500-1,000 | 1-2 hr |
| Small Commercial | <10,000 | 1,000-1,500 | 2 hr |
| Medium Commercial | 10,000-50,000 | 1,500-3,000 | 2-3 hr |
| Large Commercial | 50,000-100,000 | 3,000-4,000 | 3 hr |
| Industrial | >100,000 | 4,000-8,000 | 3-4 hr |
Design Criteria
Velocity Limits
- Normal: 2-5 ft/s
- Maximum: 8-10 ft/s
- Fire flow: 10-12 ft/s
- Avoid water hammer
Pressure Limits
- Min static: 40 PSI
- Max static: 80 PSI
- Min during fire: 20 PSI
- PRVs above 80 PSI
Pipe Sizing
- Min residential: 6"
- Min commercial: 8"
- Grid/loop systems
- Dead ends <600 ft
Appurtenances
- Valves per 500 ft
- Hydrant spacing: 300-600 ft
- Air release valves
- Blow-offs at low points