State Requirements
Washington Septic Tank Requirements
Complete guide to septic system requirements in Washington (WA). Use our calculator for personalized recommendations.
Regulatory Agency
Washington State Department of Health
Permit Required
YesProfessional Install
RequiredMinimum Tank Size
1,000 gal
Tank Size Requirements
| Bedrooms | Min Tank Size | With Garbage Disposal |
|---|---|---|
| 3 | 1,000 gal | 1,500 gal |
| 4 | 1,250 gal | 1,875 gal |
| 1-2 | 1,000 gal | 1,500 gal |
| 5-6 | 1,500 gal | 2,250 gal |
Drainfield Sizing by Soil Type
Minimum square feet of absorption area based on soil percolation rate:
Gravel/Sandy
125
sq ft minimum
Sandy
175
sq ft minimum
Loam
225
sq ft minimum
Clay
325
sq ft minimum
Washington Specific Notes
- High rainfall in western Washington
- Puget Sound areas have marine recovery requirements
- Operation and maintenance programs required
Regulatory Contact
Washington State Department of Health
Important Disclaimer
This information is provided for reference only. Local county or city requirements may be stricter than state minimums. Always verify requirements with your local health department before installation.
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