LID Rainwater Harvesting: Cisterns & Integrated Systems Guide

This technical guide covers large-scale, building-integrated rainwater harvesting (RWH) systems with underground/indoor cisterns for year-round use, emphasizing low-impact development (LID). Core components: catchment (rooftops), coarse debris screens/filters, storage cisterns, and pipe networks with roof drains. Position early in treatment trains for max reuse volume, upstream of bioretention; overflows can gravity-feed infiltration if above-grade. Planning assesses catchments: regrade large roofs for even drainage, decide on rooftop-only vs. stormwater (latter needs more treatment). Cistern siting requires soil/building load-bearing for water weight; in cold climates, drain systems pre-freeze or insulate pipes/pumps/cisterns. Pipework uses frost-proof designs, expansion joints. Sizing matches demand via spreadsheets modeling monthly balances; quality upgrades like fine filters for potable use. Tables compare catchment types (e.g., green roofs reduce volume but need less treatment). Overflow strategies: pump to downstream LID if below-grade. Maintenance: access ports for cleaning, backwashing filters. Practical for urban regenerative designs, integrates with green infrastructure for drought resilience—e.g., sub-surface irrigation from tanks. Provides specs on screens (1/16-inch mesh), cistern materials (HDPE, concrete), and pump selection. Enables engineers to implement robust, climate-adapted systems with quantified benefits like 50-90% rooftop capture.