Water performance in New Zealand office buildings

There is no formal information on overall water use in New Zealand commercial office buildings, or on how much water a building might be expected to use for a given purpose. Over the past three years this study has undertaken multiple investigations of daily water usage and patterns, as well as overall building water audits to help resolve this gap in New Zealand commercial building literature.

Water use indices (performance benchmarks) are established based on performance data from ninety-three commercial office buildings within Auckland and Wellington. Statistical analysis shows that there is a significant difference between the two cities; therefore individual benchmarks were required. The final results show that the median (typical) water usage for office buildings, based on net lettable floor area, is 0.76 m3 /m2 /year for Auckland and 1.03 m3 /m2 /year for Wellington. The reason for this difference between the two cities is hypothesised to be the higher Auckland water tariff giving incentives for reducing both water and wastewater.

The main areas for potential savings of water, and therefore expenditure, were found to be in the restrooms. The effect of Water Efficiency Labelling Scheme (WELS) rated appliances and/or higher efficiency flushing/outlet mechanisms showed a ‘noticeable’ reduction in water use, where these were implemented in buildings. The study also found that buildings harvesting rainwater did not reduce internal water demand, but rather reduced the demand on the local mains supply by using an alternate supply.