Given Data:
- Roof Area = 150 m²
- Average Annual Rainfall = 1000 mm
- Runoff Coefficient = 0.8
- Daily Water Requirement = 500 liters/day
- Duration for Storage Tank Supply = 3 months (~90 days)
- Calculate Total Rainwater Harvested per Year
2. Design the Size of the Storage Tank
Water needed for 3 months =
Storage Tank Capacity Required = 45,000 liters
You can choose to install:
- One large tank of 45,000 liters
or - Three tanks of 15,000 liters each (modular design for easy cleaning and maintenance)
3. Overflow System Design
- When rainfall exceeds storage capacity (after the tank fills), excess water should be safely diverted to avoid flooding.
- Overflow Pipe:
- Should be slightly lower than the tank rim.
- Divert water to a soak pit, recharge well, or storm drain.
- Use PVC/HDPE pipe of minimum 110 mm diameter.
4. Filtration System Design
Before Storage (Pre-filtration):
- Mesh Filter at roof outlets to block leaves and debris.
- First Flush Diverter to discard the first few liters of dirty rainwater.
During Storage:
- Store in covered tank to avoid contamination, mosquito breeding.
After Storage (Post-filtration):
- Sand-Charcoal Filter or UV Purifier if water is used for domestic purposes like drinking or cooking.
5. Overall Layout Design
Rain falls on roof
↓
Gutters collect water
↓
Mesh filters remove debris
↓
First flush diverter removes initial runoff
↓
Filtered water enters storage tank (45,000 liters)
↓
Overflow pipe diverts excess to soak pit or drain
↓
Pump system (if needed) for internal household distribution
Summary Table
| Parameter | Value |
|---|---|
| Roof Area | 150 m² |
| Average Annual Rainfall | 1000 mm |
| Runoff Coefficient | 0.8 |
| Total Rainwater Harvested | 1,20,000 liters/year |
| Storage Capacity (3 months) | 45,000 liters |
| Daily Usage | 500 liters/day |
| Filtration | Mesh filter + First Flush + Sand/Charcoal |
| Overflow System | PVC pipe to soak pit/drain |