Australia is the driest inhabited continent in the world, yet it has recorded the world’s second-highest per capita water consumption, according to a report by Melbourne-based Hydraulic Engineer CJ Arms & Associates.

The report also states that the City of Melbourne in Victoria plans a 12% reduction in the municipality’s water use by the year 2020 (based on 1999 figures), despite forecast residential population growth of 41%.

To this end, Australia’s greenest and healthiest office building, the A$77 million (US$63 million) Council House 2 – known as CH2 – with 10 stories and three basement floors, opened in the central business district in August last year. It provides office facilities for about 540 staff and includes retail spaces and underground parking.

In 2003 the Green Building Council of Australia launched the Green Star rating system, which is similar to the Leadership in Energy and Environmental Design (LEED) system in the United States.

CH2 is the first to achieve a six-star office design rating, the highest possible. It is a visionary building that harvests sunlight, cool night air, water, wind and rain.

The Green Star system separately evaluates the environmental design and performance of Australian buildings based on criteria including energy and water efficiency, quality of indoor environments and resource conservation.

The building’s hydraulic engineer and designer Christopher Arms of CJ Arms & Associates says the concept building came in for much criticism from the development community.

“They were asking: ‘Why build this style of building when it is so expensive – and for a public building?’,” Arms says.

“However, public buildings should be pushing the boundaries of design and sustainability to demonstrate what can be achieved without necessarily worrying about the developer’s margin.

“We were given the charter to do things that had not been done before, to investigate leading-edge technologies. It was a fascinating process. We had workshops on innovation, asking ‘what if’ and ‘why not’ with a lot of healthy debate. Project architect Mick Pearce was an inspiration.”

CH2 consumes only 15% of the energy of a regular building and about 30% of the water.

Initiatives include a sewer-mining plant in the basement, phase-change materials for cooling, automatic night-purge windows, wavy concrete ceilings, and a facade of louvres powered by photovoltaic cells that track the sun.

The rating assessment criteria for water include water efficiency, water substitution, water metering, cooling towers and landscape irrigation.

Water management in CH2 falls mainly into four categories: water efficiency, water reuse (rainwater harvesting and sprinkler test water reuse), water recycling and water-saving initiatives (shower towers, phase-change materials, chilled water cooling system and plant watering system).

However, the true innovation of this building lies in water extraction from the sewer running underneath. One of the many challenges in water supply is that an office building does not produce as much waste water as a residential building of the same size, so not enough waste water is generated to fully supply reuse requirements.

And in this case the building could not rely solely on rainwater because of a long-term drought in south-east Australia.

Arms says the one constant and sustainable source of water in cities is the sewer system. Sewage usually contains about 95% water, and this was where the designers looked for a supply.

About 100,000L of water a day will be extracted from the authority’s sewer main under the street outside the building, along with any greywater from inside the building.

“There is no separation of greywater and blackwater; it is all treated in the same way,” Arms says.