Cistern / Rainwater Harvesting¶

Cisterns are governed by BMP Manual Chapter 9.1 in the live source corpus. This page now stays with the source-backed center of gravity: roof-runoff capture, storage for reuse, and the requirement that retention claims depend on available storage and documented system operation rather than on generic "tank equals credit" shorthand.

Structured citation evidence for this page lives in the sibling claim manifest.

Overview¶

In the enrolled source set, a cistern is a roof-runoff capture and reuse BMP. Its stormwater value comes from storing runoff and making storage available again through reuse or drawdown before later storm events.

Source Mapping¶

The live citations layer resolves this route directly to the following canonical source bundles.

Route type: canonical
2023 source bundle: Chapter 9.1 (2023_BMP_9_1) - Cisterns
2026 source bundle: Chapter 9.1 (2026_BMP_9_1) - Cisterns

Key verified claims already tied to this page manifest: - Cisterns are roof-runoff capture and reuse BMPs in the live source set. - Cistern sizing stays tied to storage-and-reuse performance, not just nominal tank size. - In the 2026 source set, cistern GI and retention use is tied to Ch.9.1 and the new Ch.14 framework; this linkage does not exist in the 2023 source set. - Cistern maintenance remains a storage-system performance issue rather than a generic housekeeping issue.

Design Criteria¶

The reconciled design criteria below come from the live crosswalk and page-level claim set, not from the older narrative snapshot.

Parameter	2023 source value	2026 source value	Change
Storage capacity / sizing method	Must contain WQDS runoff volume without overflow; demand must empty cistern within 72 hours of rain event (based on lowest 3-consecutive-day demand)	-	unknown
Chapter 14 volumetric reduction credit	N/A - Chapter 14 did not exist in 2023 era; no volumetric reduction credit referenced in BMP 9.1 (2023)	Cistern + reuse system may qualify for volumetric reduction credit under Ch. 14	new

Source-backed criteria that still control this route: - Cisterns are roof-runoff capture and reuse BMPs in the live source set. - Cistern sizing stays tied to storage-and-reuse performance, not just nominal tank size. - In the 2026 source set, cistern GI and retention use is tied to Ch.9.1 and the new Ch.14 framework; this linkage does not exist in the 2023 source set. - Cistern maintenance remains a storage-system performance issue rather than a generic housekeeping issue.

Siting Constraints¶

The current source-backed siting review should focus on:

whether the runoff source is appropriate for rainwater harvesting
whether the project has a credible storage, overflow, and reuse strategy
whether the system can be maintained as an actual storage BMP rather than a decorative tank

Maintenance¶

Maintenance still turns on storage-system performance:

keep inlets, screens, first-flush components, and overflow paths working
inspect the tank and associated piping for blockage, leaks, or operational failure
treat loss of available storage as a direct stormwater-performance problem

Source Bundles¶

Use these source bundles when checking the live extracted text or paired OCR evidence:

2023 bundle: Chapter 9.1 (2023_BMP_9_1) - Cisterns
2026 bundle: Chapter 9.1 (2026_BMP_9_1) - Cisterns