Water is a crucial resource increasingly under stress. Yet rainfall, even in arid climates, can make up a sizable portion of any home, acreage, or farm's water requirements if harvested and utilized with care. The key is appropriate planning and high-quality site- and climate-specific design. Essential Rainwater Harvesting is a comprehensive manual for designing, building, and maintaining water harvesting systems for the warm and cold climates of the world. Presenting design considerations and approaches for the most common household rainwater supply scenario, primary, supplemental, and off-grid supply, this step-by-step approach covers. Considerations for full-property water security. Demand planning and conservation strategies. Supply calculations and design implications for extreme rainfall and drought. Materials selection and water quality. System and site assessment. Sizing and design of gutters, conveyance, tanks, and pumps. Pre-filtration, filtration, and disinfection options. System maintenance and upkeep. This practical resource provides DIYers, trades, and rainwater practitioners with the essential tools, methods, and technical know-how to design, build, and maintain rainwater harvesting systems anywhere.