Alternative water sources in New Zealand’s commercial buildings

Abstract

Rainwater harvesting and greywater recycling are two potential measures to make significant reductions in commercial building water use in New Zealand. Rainwater harvesting involves the collection of water from roofs during rainfall events, while greywater recycling is the reuse of water from hand basins and showers for use in toilets and urinals. The feasibility of these systems was investigated via three areas of focus: drivers and barriers; system operation; savings to the water network. Initial results show volumetric wastewater tariffs are primary drivers for water efficiency and conservation. However, a lack of consistent regulation, perceived risks of water quality issues and loss of space for storage are perceived as barriers. Case-study buildings showed that, in locations where both water and wastewater are charged volumetrically, the relative benefit–cost comparisons were judged as acceptable by building management. Where only water is charged volumetrically (with wastewater based on annual rating valuations), this was less favourable. Water quality tests showed only minimal imperfections. Concerns appear to be largely an issue of perceived risk rather than actual risk. Together with site visits, the water quality testing has contextualised valuable feasibility, design and operational opportunities. The savings to the water networks, however, appear to be minimal.