Rainwater harvesting collects and stores rain from your roof for later use in gardens, lawns, car washing, and (with proper treatment) indoor non-potable uses. It is legal in all 50 US states, though regulations vary.
17 steps across 2 sections
1. Steps Process
- Check local regulations — Contact your city/county planning office, water authority, or state environmental agency. Most areas allow simple rain barrels without permits. Larger systems, underground...
- Calculate your collection potential — Multiply roof area (sq ft) x rainfall (inches) x 0.623 = gallons collected. A 1,500 sq ft roof in an area with 1 inch of rain collects ~935 gallons.
- Choose your system type:
- Rain barrel (50-100 gallons): Simple, affordable, good for small gardens
- Above-ground tank (100-2,500 gallons): More storage, needs a flat pad
- Underground cistern (500-10,000+ gallons): Maximum storage, hidden from view, requires professional installation
- Install gutters and downspouts — Ensure your roof has properly sized gutters directing water to collection points. Clean gutters thoroughly before installation.
- Add a first-flush diverter — This critical component diverts the first 1-2 gallons of rainfall (which contains the most contaminants from the roof) away from the storage tank.
- Install leaf screens and filters — Place mesh screens on gutters and a filter on the downspout to keep debris, leaves, and insects out of the tank.
- Set up the storage container — Place on a stable, level surface. Elevate rain barrels on cinder blocks for gravity-fed use. Connect the downspout to the tank inlet. Install an overflow outlet direc...
2. Key Details
- Legal in all 50 states (some restrictions on volume or use in Colorado, Utah, and a few others)
- Basic rain barrel: $50-$200; cistern systems: $1,000-$10,000+
- States with incentives: Texas (exempts rainwater equipment from sales tax), Oregon, California, Virginia, and others
- Uses: garden irrigation, lawn watering, car washing, livestock, toilet flushing (with proper plumbing and permits)
- NOT safe for drinking without proper filtration and treatment (UV, chlorine, or reverse osmosis)
- Mosquito prevention: keep tanks sealed, use fine mesh screens, add BTI dunks to standing water
- Winter: in freezing climates, drain rain barrels before winter or use insulated/heated systems
Common Mistakes
- Not checking local regulations first
- Skipping the first-flush diverter (collects the dirtiest water)
- Not using mosquito screens (creates breeding habitat)
- Placing rain barrels on unstable surfaces (a full 55-gallon barrel weighs 450...
- Not planning for overflow (can cause foundation damage)
Pro Tips
- Dark-colored tanks prevent algae growth by blocking light
- Connect multiple rain barrels in series for more storage
- Use a soaker hose or drip irrigation connected to the rain barrel for efficie...
- Rain gardens can handle overflow and further filter water
- Some municipalities offer free or discounted rain barrels — check with your l...