Cistern Systems: Detention, Storage & Reuse for Water Security
TL;DR: Implement cistern systems for stormwater detention, rainwater harvesting, and re-use to boost water resilience and reduce municipal reliance.
- Cistern design integrates sizing, tank types, treatment, and backflow prevention.
- Mass balance and a 90-day safety factor optimize storage volume.
- Tank options range from underground concrete to above-ground plastic.
- Treatment varies by use, from UV for potable to sediment filters for irrigation.
- Backflow prevention is crucial when integrating with municipal water supplies.
Why it matters: Effective cistern design provides comprehensive water management solutions, enhancing drought resilience and promoting self-sufficiency for non-potable uses like irrigation and toilet flushing.
Do this next: Calculate your daily water demand and potential rainfall catchment to size a cistern system for non-potable uses.
Recommended for: Experienced permaculturists, homesteaders, and designers seeking to implement advanced rainwater harvesting and greywater reuse systems.
This PDF document outlines comprehensive system design for cisterns in rainwater harvesting, covering sizing, tank types, treatment, backflow prevention, and real-world implementations for non-potable uses like irrigation and toilet flushing, with drought resilience via safety factors. Key methods start with mass balance for total storage volume, pumping for peak demand, and a 90-day minimum safety factor to buffer droughts. Tank types include underground concrete (cast-in-place or pre-cast), fiberglass, partial-bury plastic, aboveground plastic/steel, or integrated basements, with structural considerations for geotechnical and seismic loads. Treatment varies by use: potable systems require 20-micron then 5-micron filtration, UV disinfection, and point-of-use filters for taste/odor, especially from asphalt roofs; irrigation/toilet systems need sediment filters to protect equipment, possibly ozone for aesthetics. Cross-connection control is critical when backing up with city water—using reduced pressure (RP) devices, air gaps, or backflow preventers, which need permits, annual testing, and are primary regulator concerns. A case example details a 34,000-gallon central cistern for non-potable uses (toilet flushing, clothes washers, irrigation) with city backup, employing a 5-micron sand filter. Practical details include source control for roof catchment (e.g., avoiding asphalt for potable), first-flush implied via sediment management, and integration with pumps/boosters. For regenerative/self-sufficiency, this enables closed-loop water cycles, reducing municipal reliance and enhancing drought resilience through oversized storage (90-day factor) and filtration for reuse. Insights highlight code compliance for backflow, filtration sequencing, and structural engineering, providing concrete steps for permaculture sites: calculate demand, select tank type per site, install treatment train, ensure air gaps. This goes beyond basics, offering actionable specs for practitioners building resilient systems.