Household Rainwater: Cistern Sizing & Water Supply Guide
TL;DR: Properly sizing your rainwater cistern is crucial for efficient household water supply, balancing storage needs with practical and environmental factors.
- Cistern size depends on household occupancy and local rainfall.
- Avoid oversizing tanks; 10,000 gallons is often maximum.
- Underground tanks offer year-round access and prevent algae.
- Elevate tanks for better water pressure.
- Consider above-ground vs. underground based on climate.
Why it matters: Appropriate rainwater harvesting system design ensures a reliable and sustainable water source, reducing reliance on municipal supplies and improving drought resilience.
Do this next: Assess your household water needs and local rainfall patterns to estimate your ideal cistern size.
Recommended for: Homeowners, permaculture designers, and anyone interested in establishing a robust and efficient residential rainwater harvesting system.
This resource from rainwater harvesting experts provides practical guidance on cistern sizing and tank selection for residential household water supply applications. The sizing recommendations are based on household occupancy and regional rainfall patterns, offering a rule of thumb for areas that receive regular rainfall: install a 5,000 to 7,000 gallon tank for a family of four or more people, and up to a 5,000 gallon tank for households with fewer than four people. These sizing recommendations balance the desire to maximize water storage with practical constraints and efficiency considerations. The guide cautions against oversizing collection tanks, noting that there is a threshold beyond which larger tanks become counterproductive. The recommendation is to avoid installing tanks larger than 10,000 gallons unless the property is located in a region with distinct wet and dry seasons where extended storage is necessary for drought resilience. The resource addresses both above-ground and underground rainwater collection approaches, highlighting specific advantages of underground cistern installation, particularly for colder regions of the United States. Underground storage provides year-round water availability if the property has uses for collected rainwater throughout all seasons, as water stored below the frost line remains accessible even during winter months. Underground cisterns also provide environmental benefits by removing rainwater from direct sunlight, which significantly slows and eventually eliminates algae growth and reduces bacterial proliferation. Additionally, underground storage systems allow property owners to utilize ground space more efficiently and conceal the rainwater harvesting infrastructure from view, providing aesthetic and practical advantages. The guide emphasizes that water pressure is a critical factor in system performance and is directly related to tank elevation. Higher elevation of rainwater tanks and barrels produces greater water pressure in the distribution system. The resource notes that elevated tanks can achieve excellent pressure similar to dedicated water towers. For situations where elevation is not feasible, water pumps can be installed to artificially increase water pressure and maintain adequate flow rates for household applications.