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Reduce potable water demand by deploying a system to collect and store rain water from roofs, terraces and other permeable horizontal surfaces such as sidewalks and plazas. Uses for rainwater include irrigation and sewage conveyance.

Collected water passes through a filter and is stored in underground or roof top cisterns. Cisterns can occupy unusable spaces in underground parking garages and can be combined to volumes 2 to 3 stories tall. Other components include pumps and overflow drains that are connected to the sewer line. Rainwater catchment systems can also incorporate bioswales and retention ponds. On larger scale developments these site features have the added benefit of providing wildlife and plant habitat.

Estimate water needs for the building. Determine available rainfall for the building and multiply by 0.7 for “dry” year approximation. Calculate required cistern volume and select cistern location. Concurrently, specify low-flow plumbing appliances and fixtures to reduce water demand. Low flow fixtures can cut water demand by 25 to 50 percent compared to conventional fixtures. (Source: Big-box retailers, such as Wal-Mart, are currently exploring and using rainwater storage systems.

Separate conveyance infrastructure required for reclaimed water (“purple pipe”) increases the 1st cost or rainwater catchment systems. However, water savings of 50% or more help to offset that cost. In addition, costs associated with potable water supply and sewer infrastructure are projected to escalate with accelerated effect in developing countries.

Rainwater catchment systems provide non-potable water to use for low grade tasks, reserving potable water for higher grade tasks and reducing potable water demand. Rainwater catchment systems also reduce stormwater loads and associated utility costs.

Rainwater storage and conveyance infrastructure is independent of and in addition to potable water supply infrastructure. Annual rainfall seasons must be verified with respect to durations and periods. Projects in climates with extreme rainfall patterns require economic evaluation. Underground cisterns provide higher stability of water temperature and prevent freezing.

1.4.9 Green Roofs; 1.4.10 Green Walls; 1.4.11 Urban Farming; 2.1.2 Greywater and Water Recycling; 2.2.1 Water Efficient Appliances; 2.2.2 Xeriscaping ; 3.1.0 Waste Water Treatment; 3.1.2 Living Machines