OT_036: Pollard (2022) — Residential Water Use in New Zealand (BRANZ SR469)

OT_036: Pollard (2022) — Residential Water Use in New Zealand (BRANZ SR469)

Source

https://www.branz.co.nz/pubs/research-reports/sr469/ — original source (opens in a new tab; the file is not redistributed)

Summary

BRANZ Study Report SR469 (Pollard, 2022) is the first national-scope measurement of how much water New Zealand homes actually use. Earlier BRANZ work (WEEP, Kāpiti, 12 houses; AWUS, Auckland, 51 houses) was confined to single regions; SR469 recruited councils and water authorities nationwide to obtain a 66-household sample with high-resolution (10-second-interval) metering, an occupant survey, and a detailed water-appliance inventory. The headline is a NZ per-person residential water-use baseline — median 159 L/person/day in winter and 231 in summer — with the report stressing that the distribution is right-skewed (a few heavy users pull the mean well above the median), so the median is the better “typical household” figure. For Neobiome Intelligence it directly resolves the water-demand gap (RT_078): the person_water_demand_l_day cell in ③ now has an authoritative NZ value rather than an overseas proxy.

Key claims

- claim: "First national-scope NZ residential water-use study: a 66-household sample with total water use logged at 10-second intervals, plus an occupant survey and a detailed inventory of water-using appliances/fittings; recruited via councils and water-supply authorities nationwide. Builds on and supersedes the single-region predecessors WEEP (Kāpiti, 12 houses, 2007) and AWUS (Auckland, 51 houses, 2010)."
  source_location: "Abstract p.ii; Preface p.i; Methodology §3 (p.9-11)"
- claim: "Median residential water use = 159 litres/person/day (winter) and 231 litres/person/day (summer). The report recommends the median over the average because the distribution is right-skewed by a minority of high-use households."
  source_location: "Abstract p.ii; Executive Summary p.1 (median figures); §4 Results"
- claim: "Average (mean) residential water use = 213 litres/person/day (winter) and 292 litres/person/day (summer) — 34% and 26% above the respective medians, reflecting the skew toward high-use households."
  source_location: "Executive Summary p.1"
- claim: "Median household water use = 435 L/day (winter) and 504 L/day (summer); mean household use = 544 L/day (winter, SD 467) and 735 L/day (summer, SD 597)."
  source_location: "§4 Results and discussion — Total water use (p.16-18)"
- claim: "Fewer than 10% of households had a rain tank of any size (large rainwater-harvesting potential), and around 28% had a sprinkler/irrigation system (outdoor irrigation can be a large component of summer use)."
  source_location: "Executive Summary p.1"
- claim: "MBIE has a residential water-use efficiency target of 75 litres/person/day; a Watercare–Fletcher Living pilot ('the 1.5-degree home') aims to achieve it with water-saving technologies."
  source_location: "§2 Previous studies (p.7), citing MBIE (2020)"
- claim: "Context: NZ has the fourth-highest per-capita water availability in the OECD (after Canada, Iceland, Norway), but most regions have at least one fully/over-allocated river or aquifer; irrigation is the main consumptive freshwater use (dairy-cattle numbers +69% 1994-2015; total irrigated land +~70% 2002-2017)."
  source_location: "§1 Introduction (p.3)"
- claim: "Appliance/behaviour findings: ~36% of households had a (more water-efficient) front-loading washing machine — a water-savings opportunity; awareness of the Water Efficiency Labelling Scheme (WELS) was low among respondents."
  source_location: "Executive Summary p.1; §4.4 Water uses"

Neobiome Intelligence relevance

• ③ person_water_demand_l_day (resolves RT_078) — supplies the authoritative NZ per-person residential water demand: median 159 L/p/d (winter) / 231 (summer), replacing the overseas 203 L/capita/day proxy LIT_008 the wiki previously carried. The report’s own guidance — use the median, not the mean — means the model should take ~159–231 L/p/d (season-dependent), not the skew-inflated 213–292 averages OT_036. The MBIE 75 L/p/d efficiency target is the natural high-efficiency design scenario for a water-conscious community build.
• D03 Water, Waste & Circular — the demand side that the wiki’s rainwater supply data (CR_016 cost/yield; OT_030 rainfall) must meet. With ~65% of household need meetable from roof (CR_016) and a median household demand of ~435–504 L/day, OT_036 lets the rainwater tech be sized against a real NZ demand figure rather than an assumption OT_036. The <10% rain-tank prevalence quantifies the headroom for the rainwater intervention.
• I07 Fulfilment of Basic Needs — a NZ water self-sufficiency baseline at the household scale: the WSR (water self-sufficiency ratio) denominator Q_td (total demand) now has a NZ-grounded value, where it previously relied on overseas or Swedish baselines OT_036.

Research targets

Documents to retrieve

• The companion U. Auckland end-use disaggregation report (Whittaker, Scott & van Zyl) — the per-fixture (toilet / shower / tap / washing-machine) L/day split that SR469 itself did not produce; needed if the NI water model ever sizes demand-side efficiency measures by fixture rather than in aggregate. In the interim the earlier BRANZ WEEP study OT_227 (Heinrich 2007, Kāpiti, n=12) supplies a retrievable NZ per-fixture table — the basis for the water model’s potable/non-potable split.
• BRANZ SR (Garnett & Sirikhanchai, 2018) residential water-tariff study — the cost/tariff companion to this use study, relevant to D03/I01 water-cost reasoning.

Research gaps

• Regional disaggregation of per-person demand (the 66-household national sample is not robust at single-region resolution) — the model currently treats person_water_demand as a national constant in ③, which SR469 supports, but a regional split would refine dry-region (e.g. Tasman) sizing.
• A per-occupancy curve (L/household/day vs household size) — SR469 reports per-person and per-household separately but the model’s per-person constant assumes linearity across household sizes.

Connections

Links to

Sources (4): CR_016 · LIT_008 · OT_030 · OT_227

Referenced by

Sources (4): OT_040 · OT_123 · OT_124 · OT_227

Technologies (2): Greywater Recycling · Rainwater Harvesting (Roof Collection & Dual R…

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

SSI indicators (1): I07: Fulfilment of Basic Needs