Graywater System Calculator
Size graywater collection and distribution systems
Graywater Sources
Irrigation Area
System Requirements
Daily Graywater Generation
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Surge Tank Size
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Weekly Volume
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Application Rate
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Min. Mulch Basin Area
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Distribution Pipe
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System notes will appear here.
Graywater Generation Rates
| Source | GPD/Person | Notes |
|---|---|---|
| Shower/Tub | 15-25 GPD | Varies by duration |
| Bathroom Sink | 3-5 GPD | Per occupant |
| Clothes Washer | 10-15 GPD | Per household avg |
| Kitchen Sink | 5-8 GPD | May contain grease |
Code Requirements
- No surface ponding or runoff
- 24-hour surge tank maximum
- Subsurface distribution only
- Not for spray irrigation
- 2" minimum mulch cover
- Overflow to sewer/septic
- 3-way diverter valve required
System Types & Applications
Laundry to Landscape
- Simplest system
- No tank required
- Direct to mulch basins
- Permit-exempt in CA
- 1" PE distribution pipe
Branched Drain
- Gravity-fed system
- Multiple sources
- Splitting chambers
- No pump needed
- 2" minimum drain pipe
Pumped System
- Surge tank required
- Submersible pump
- Drip or subsurface
- Pressurized distribution
- Filter required
Treatment System
- Commercial applications
- Filtration + disinfection
- Toilet flushing allowed
- NSF 350 certified
- Higher maintenance
Soil Percolation Rates
| Soil Type | Perc Rate (min/inch) | Loading Rate (GPD/sq ft) | Min Basin Area/GPD |
|---|---|---|---|
| Gravel/Coarse Sand | <1 | 1.2 | 0.83 sq ft |
| Sandy | 1-5 | 0.8 | 1.25 sq ft |
| Sandy Loam | 6-15 | 0.6 | 1.67 sq ft |
| Loam | 16-30 | 0.45 | 2.22 sq ft |
| Clay Loam | 31-60 | 0.3 | 3.33 sq ft |
| Clay | >60 | 0.2 | 5.0 sq ft |