Water system design at community scale involves the same fundamental hierarchy as individual building design — harvest, store, use, infiltrate — but with larger volumes, more users, and more complex distribution and treatment requirements.

Community rainwater harvesting aggregates collection from all rooftops and potentially from land-based catchment areas (hardened paths, sealed shallow ponds) into shared storage infrastructure. The advantage of aggregated storage is resilience: a large central cistern can buffer the community through extended dry periods more effectively than many small household cisterns.

Community water distribution requires a pressure system with appropriate treatment. At minimum, a sediment filter and ultraviolet sterilizer are required for potable water. More sophisticated systems may include membrane filtration or sand filtration for high-turbidity source water. The distribution system should be designed with zones (potable water to kitchens and bathrooms; untreated water to irrigation) to minimize the cost of full treatment for all uses.