OT_039: BRANZ Bulletin 664 (2021) — Residential Rainwater Systems

OT_039: BRANZ Bulletin 664 (2021) — Residential Rainwater Systems

Source

https://www.branz.co.nz/pubs/bulletins/bu664/ — original source (opens in a new tab; the file is not redistributed)

Summary

BRANZ Bulletin 664 (2021) is the practical design-and-compliance guide for residential rainwater collection in New Zealand — covering collection area, storage, filtration, treatment, building-consent thresholds, and the rules separating potable from non-potable supply. It is a design guide, not a cost study, so it adds no pricing; its value for Neobiome Intelligence is twofold: it corroborates the model’s rainwater runoff coefficient (its sizing rule assumes only 10–20% collection loss, i.e. ~0.80–0.90, with 0.8 the conservative figure the model uses), and it supplies the regulatory/design constraints for sizing a community rainwater system — the consent-free tank-volume schedule and the treatment standards required before roof water can be used as drinking water.

Key claims

- claim: "BRANZ Bulletin 664 (Aug 2021) is the NZ design-and-compliance guide for residential rainwater systems, covering collection area, storage, filtration/treatment, building consent, and potable vs non-potable use. Rainwater can meet all of a home's water needs (including drinking) if adequately filtered and treated; many NZ homes already rely on roof rainwater where mains is unavailable."
  source_location: "§1 Introduction"
- claim: "Sizing rule: when calculating how much rainwater can be collected, assume around 10–20% loss through spillage and evaporation (i.e. ~80–90% collection efficiency); the collectable volume depends on the local average rainfall and the roof collection area."
  source_location: "§3.0.3"
- claim: "Consent-free storage (Table 1): water-storage tanks not requiring a building consent are up to 35,000 L if supported directly on the ground; 16,000 L if no more than 0.25 m above ground; 8,000 L (≤0.5 m); 4,000 L (≤1 m); 2,000 L (≤2 m); 1,000 L (≤3 m)."
  source_location: "Table 1 (p.2)"
- claim: "Potable rainwater: the system must use materials meeting AS/NZS 4020:2018 (products in contact with drinking water); BRANZ recommends meeting the Drinking Water Standards for NZ 2005 (revised 2018), though these are not mandatory for private households; a building consent is required for new installations. A potable treatment train uses a leaf/debris strainer + first-flush diverter + sediment cartridge filter + UV (or chlorine) disinfection."
  source_location: "§2.2 + §3–4 (Figures 1, 5)"
- claim: "Non-potable supply must be clearly labelled (lilac-coloured piping) per AS/NZS 3500.1:2021, NZS 5807:1980 and Building Code G12/AS1; non-potable pipes must not be located where food is processed or above potable water; an approved backflow-prevention device is required where connected to a potable/mains system."
  source_location: "§2.1.x, §2.3"
- claim: "Benefits of rainwater collection include reduced mains demand and stormwater load, water where no mains supply exists, savings on metered supply, and increased household and community resilience during drought, water restrictions, and natural disasters when mains may be cut off or contaminated."
  source_location: "§1.0.3"

Neobiome Intelligence relevance

• D03 — rainwater tech runoff coefficient (corroboration). The model’s rainwater flow produces @rainfall_mm × 0.8 (runoff 0.8). Bulletin 664’s sizing rule — assume 10–20% collection loss — independently supports a collection efficiency of 0.80–0.90, confirming 0.8 as the conservative-correct value with a BRANZ primary (matching CR_016’s 75–90% / “use 0.80”) OT_039.
• D03 — sizing/consent constraint. The consent-free tank schedule (≤35,000 L ground-supported, falling to 1,000 L at 3 m elevation) is a real design constraint on community rainwater storage: storage above 35,000 L — or any elevated tank above the height bands — triggers a building consent. This is the BRANZ primary behind CR_016’s “35,000 L largest no-consent tank” claim OT_039.
• D03/I07 — potable vs non-potable regulatory layer. The AS/NZS 4020 + Drinking Water Standards + treatment-train requirements quantify what it takes for community roof water to be potable vs non-potable — directly the regulatory friction an interviewee described (Interview VI [INT_006]: collecting rainwater for more than one household triggers a heavier public-health treatment regime). Seeds the rainwater_harvesting technology page OT_039.
• ⚠ Scope: no cost data — the rainwater capex cell stays with CR_016 (RT_184).

Research targets

Research gaps

• The NZ first-flush diverter sizing rule (litres per m² of roof) and the recommended sediment-filter micron rating + UV dose for potable rainwater — design parameters the bulletin describes qualitatively but does not fully quantify; needed if the NI model ever sizes the treatment train and its cost.
• Whether the Tasman/Lower Moutere pilot’s collective (multi-household) rainwater reticulation crosses the “public supply” threshold that triggers the heavier Drinking-Water-Standards treatment regime (the int_006 regulatory question, restated for the pilot).

Connections

Links to

Sources (1): CR_016

Technologies (1): Rainwater Harvesting (Roof Collection & Dual R…

Referenced by

Sources (2): CR_016 · OT_124

EDT domains (1): D03: Water, Waste & Circular Systems

Technologies (1): Rainwater Harvesting (Roof Collection & Dual R…