Install a professional underground cistern system

For serious water independence, a buried polyethylene or concrete cistern stores 1,000-10,000 gallons underground, out of sight and frost-protected. A pump delivers water on demand at household pressure.

System Components

• Cistern tank: Polyethylene (1,500-2,500 gal: $800-2,000) or poured concrete (3,000-10,000 gal: $3,000-8,000). Poly is lighter and cheaper; concrete lasts 50+ years.
• First-flush diverter: Diverts the first 1-2 gallons of dirty roof water per 1,000 sq ft of roof.
• Leaf screen and downspout filters: Pre-filter large debris before water enters the cistern.
• Pump: A 1/2 HP shallow well pump ($150-300) delivers 20-40 PSI, sufficient for sprinklers and drip irrigation.
• Float valve or level indicator: Prevents overflow and shows remaining capacity.

Professional Installation

Hiring a contractor for excavation and plumbing typically costs $2,000-5,000 on top of equipment. Total installed cost for a 2,500-gallon system: $4,000-8,000.

Tips

• A 2,500-gallon cistern on a 2,000 sq ft roof in an area with 30 inches annual rainfall will fill 7-8 times per year
• Underground tanks stay cool (40-55°F year-round), inhibiting algae and bacteria growth
• Check local building codes — some jurisdictions require permits for underground water storage