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 Rainwater harvesting & greywater recycling

Nearly all of New Zealand's non-residential buildings are totally dependent on the water reticulation network. Treated potable water is used for hygiene, conditioning and other purposes, including irrigation and toilet flushing. An increasing number of building and facilities managers want to understand the feasibility of installing alternative water sources into their non-residential buildings. As shown in Christchurch, where 80% of the city's water and sewerage network was severely damaged in the 2011 earthquakes, there is also a need for greater water resilience in our buildings. This is where independent water supply systems, such as rainwater harvesting and greywater recycling could be effective. The application of these systems also has implications on the wider network.

Feedback from a number of designers suggest higher targets are now being frequently considered. There is currently no New Zealand specific guidance to assist and ensure delivery solutions will work effectively in this area.

BRANZ has commenced research to develop a rainwater harvesting and greywater recycling framework for New Zealand. This research will conclude on 31st March 2017. The aim is to provide information to increase industry knowledge on rainwater harvesting and greywater recycling systems for non-residential buildings, including operational and financial feasibility and for both new buildings and retrofits. The work will also be informed by international standards, guidance and best practice and link to existing and developing New Zealand structures and programmes as far as possible.

In order to create a holistic overview of the rainwater harvesting and greywater recycling system feasibilities, a multi-disciplinary case study approach will be undertaken utilising engineering, environmental, social and economic expertise. This will be achieved through an Advisory Panel and the three research streams:

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Through literature review, workshopping with the Advisory Panel and industry stakeholder engagement, the first edit of a New Zealand Strategic Framework has been developed. This identifies ten measurables across the three research streams, scoring from worst (1) to best (5).


Knowledge: quality evidence-based information available on rainwater and greywater systems and opportunities.
Awareness: general understanding of water use, water efficiency and conservation and wastage consequences.
Consistency: standardised charging mechanisms, policy and guidelines for water across New Zealand.
Management: effective management of buildings and their water systems.
Installation: deliver building and infrastructure systems according to their design and legislation.
Affordability: products, equipment and service relating to rainwater harvesting and greywater recycling in buildings are affordable.
Transparency: feasibility metrics are significantly improved.
Communication: make communication with building industry commonplace.
Measurement: measure through volumetric water and wastewater metering.
Security: maintain a secure water supply for all of New Zealand.

From this programme, the following outputs will be produced:
• Finalised strategic framework for industry to progress towards integrated water sustainability through rainwater harvesting and greywater recycling systems.
• Calculation model to aid in determining the feasibility of implementing rainwater harvesting and greywater recycling non-residentially.
• Assessment of the impacts on the three water networks (water, wastewater and stormwater).
• Design guidance booklet.
• Report of water quality in five of the case study buildings, measured over 12 months.
• Publications, including a BRANZ study report, BUILD and WATER articles.

Project publications to-date:
• BUILD - rainwater and greywater
• BUILD - water views

Please contact Dr Lee Bint for any further information or to discuss how you can get involved.