Rainwater harvesting: roof drainage to cisterns for non-potable use (irrigation, toilets); 1000+ gal typical residential

Description

Roof runoff captured to a cistern or rain barrel + used for non-potable purposes: landscape irrigation, toilet flushing (with separate purple-pipe distribution), washing machine. Typical residential cistern: 500-5000 gal, above- or below-grade. First-flush diverter removes the first ~½ in of runoff (carries roof contaminants). Backflow prevention required between potable + non-potable systems. Local code varies — some jurisdictions require permits + dual plumbing for indoor use.

Why this exists

A 2000-sqft roof in NY (~40 in annual rainfall) collects ~50,000 gal/year — enough to cover most irrigation + significant toilet-flushing demand. Architects designing for sustainability + water-efficiency should integrate the cistern + plumbing routing into the schematic design.

Categories

Source

Solver enforcement

Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.

Related directives

• Exterior ramps: maximum slope 1:12, minimum 36 inch clear width · HUD FHA Design Manual Chapter Two §2.7
• Build to the latest natural-hazard-resistant code edition · FEMA P-2325 §Building Codes Basics
• Coastal-pile foundations should embed deeply to resist erosion + uplift · FEMA P-2325 §Florida Building Code / Sand Palace lessons
• Lowest floor at or above Base Flood Elevation in Special Flood Hazard Areas · FEMA P-2325 §Flood Hazard Provisions
• In WUI zones, protect openings from wind-blown embers · FEMA P-2325 §Wildland-Urban Interface (WUI)