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scenarios and using ‘observed’ and ‘opti- mistic’ supply scenarios (see Table 1). Forecast savings for optimistic scenario Assuming, under the ‘optimistic’ scenario, that all non-potable water could be sourced from rainwater, potentially 23% of total water from the water network could be saved. This equates to a nancial saving for both the building owner and the water service provider.
Rainfall used for non-potable purposes is not required to be treated, saving the cost of treating and transporting potable water that is ushed down the toilet. However, storage must be provided.
Using an ‘optimistic’ scenario where 23% of total water demand is supplied by rain- water and greywater sources, the forecast savings across all four regions were:
● low uptake – 109,859 kL/year (in Bay of
Plenty) to 585,814 kL/year (in Auckland)
● medium uptake – 235,462 kL/year (in Bay of Plenty) to 1.5 million kL/year (in Canterbury) ● high uptake – 580,782 kL/year (in Bay of Plenty) to 3.6 million kL/year (in Canterbury).
Forecast savings for observed scenario
When the buildings were aggregated per region, the volume of non-potable demand that is able to be supplied varies (see Table 1). Accordingly, a second supply scenario was used to project future impacts to the water networks, based on ‘observed’ supply at the regional scale (see Figure 2).
Using an ‘observed’ scenario per region the forecast savings across all four regions were: ● low uptake – 199,743 kL/year (in Bay of
Plenty) to 925,170 kL/year (in Canterbury) ● medium uptake – 428,112 kL/year (in Bay of Plenty) to 2.6 million kL/year (in Canterbury) ● high uptake – 1 million kL/year (in Bay of Plenty) to 6.2 million kL/year (in
Canterbury).
Design lessons
The site investigations, as-built documenta- tion, discussions with building managers and users and analysis of monitored water data resulted in several design lessons. For operational efficiency, the three most significant were:
● ease of use for monitoring and switch- over of mains to rainwater or greywater use is necessary
● storage and distribution could be better designed to reduce additional energy, pumping and pipe costs
● education is necessary, particularly for building management and staff, and maintenance requirements.
For more Three study reports on this work
are available at www.branz.co.nz/rwhgwr. Alternatively, email [email protected] for more information.
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84 — August/September 2017 — Build 161