OK State Rainwater Harvesting: Design & Sizing Guide
TL;DR: Engineer a precise rainwater harvesting system for any scale using formulas and component specifications for reliable water supply.
- Calculate precise rainwater catchment and storage needs.
- Select appropriate components for conveyance and delivery.
- Implement first-flush diverters for water quality.
- Size cisterns to buffer dry spells and meet demand.
- Optimize system layouts for efficiency and resilience.
Why it matters: Precise rainwater harvesting design ensures sustainable water management, reducing reliance on external sources and enhancing drought resilience for various applications.
Do this next: Assess your average monthly water demand and available roof catchment area to estimate potential water savings.
Recommended for: Designers, engineers, and homesteaders seeking comprehensive technical specifications for building robust rainwater harvesting systems.
This fact sheet from Oklahoma State University Extension provides engineering-focused design and sizing for rainwater harvesting systems at home, commercial, or community scales, with formulas, examples, and component specs for practical deployment. Five main components: (1) conveyance (gutters/downspouts), (2) storage (cisterns sized for demand peaks), (3) overflow, (4) outlet, (5) delivery/pumping. Optional first-flush diverter improves quality by diverting initial runoff. Catchment uses roof footprint (not surface area), prioritizing proximity to cistern to shorten pipes. Sizing formula: G = 0.6 × P (monthly precip inches) × A (roof sq ft) × E (system efficiency, 0.8-0.9, reduced by overflows). Example: For 1,500 sq ft vegetable garden needing 1 inch/week (June-Sept), 4,500 gal/month demand requires 1,100 sq ft catchment storing peak rain for irrigation-first, then municipal backup. Lists items: gutters, downspouts, 5,000-gal cistern, first-flush, pump, filters. Emphasizes uneven precip/demand, so cisterns buffer dry spells for drought resilience. Conveyance efficiency drops in intense rains due to gutter overflow. Delivery options: gravity or pumps. This delivers concrete calculations, real-world example with bill of materials, and optimization for permaculture irrigation, ensuring systems meet specific water needs reliably.