Using Harvested Rainwater for Lawn Irrigation
Maintaining a healthy lawn of approximately 1,000 square feet requires roughly 75 gallons per day during the growing season — more in hot, dry climates and less in cooler, humid regions. Lawns are the largest consumer of residential water in many communities, accounting for 30-60% of household water use during summer months. Using harvested rainwater for lawn irrigation can dramatically reduce your municipal water bill. Most turf grasses need about 1 inch of water per week, which translates to 623 gallons per 1,000 square feet. An automated sprinkler system connected to your rainwater tank provides the most consistent coverage. Consider reducing lawn area or switching to drought-tolerant grass varieties to decrease demand.
Lawn Irrigation Potential by State
How much of your lawn irrigation demand can rainwater meet? It depends on where you live. The table below shows the annual harvest, demand coverage, and recommended tank size for lawn irrigation in eight representative states, using a 1,500-square-foot asphalt shingle roof .
| State | Annual Rainfall | Annual Harvest | Demand Met | Rec. Tank | Savings/Year |
|---|---|---|---|---|---|
| California | 22.2" | 13,756 gal | 85.7% | 5,000 gal | $123.80 |
| Texas | 28.9" | 22,277 gal | 100.0% | 2,500 gal | $80.25 |
| Florida | 54.5" | 39,622 gal | 100.0% | 5,000 gal | $80.25 |
| New York | 46.2" | 33,641 gal | 100.0% | 5,000 gal | $144.45 |
| Colorado | 15.9" | 11,589 gal | 72.2% | 1,000 gal | $57.95 |
| Hawaii | 63.7" | 45,229 gal | 100.0% | 5,000 gal | $240.75 |
| Arizona | 13.6" | 8,373 gal | 52.2% | 1,000 gal | $50.24 |
| Washington | 38.4" | 27,511 gal | 100.0% | 5,000 gal | $96.30 |
Setup Requirements for Lawn Irrigation
Lawn irrigation requires more infrastructure than garden watering because sprinkler systems demand consistent water pressure (20-40 PSI) that gravity-fed systems cannot provide. You will need a storage tank of at least 1,000 gallons, a pump capable of 10-15 GPM, and a pressure tank to maintain consistent flow. Many homeowners connect their rainwater tank to their existing in-ground sprinkler system through a transfer pump and pressure switch.
A dual-source controller is the most practical approach: the system draws from your rainwater tank first, and automatically switches to municipal supply when the tank runs low. This ensures your lawn is always watered while maximizing rainwater usage. Install a float switch in the tank to signal the controller when water levels are insufficient. Consider converting to low-water-use grass varieties or replacing portions of your lawn with native plants to reduce demand significantly.
Recommended Equipment
- Storage tank (1,000-2,500 gal)
- Transfer pump (10-15 GPM, 40 PSI)
- Pressure tank
- Dual-source controller or manual switchover valve
- Float switch for low-level shutoff
- First-flush diverter
Other Rainwater Uses
Explore other ways to use harvested rainwater at home:
- Garden Irrigation — 50 gal/day
- Toilet Flushing — 20 gal/day
- Laundry — 15 gal/day
- Car Washing — 50 gal/day
- Livestock Watering — 30 gal/day
- Pool Top-Off — 10 gal/day
- Drinking and Cooking — 1 gal/day (potable treatment required)
- General Outdoor Use — 30 gal/day
- Pressure Washing — 100 gal/day
Calculate Your Lawn Irrigation Potential
Use our Rainwater Harvesting Calculator to see how much of your lawn irrigation demand can be met by rainwater in your specific location. Select lawn irrigation from the use checkboxes along with any other uses you are considering, and get a personalized monthly supply vs. demand analysis with tank size recommendation and cost savings estimate.