Offices could cut urban consumption four per cent.

Huge water savings could be realised if Australia’s office towers would simply minimise waste and use greywater, writes Guenter Hauber-Davidson.

Large office buildings can consume between 15,000-50,000kL of fresh potable water per annum. In total, they are estimated to make up 12-15 per cent of urban water use in Australia. If 30 per cent of this could be saved, as proven in many projects, then Australia’s total urban water consumption could readily be reduced by four per cent. There are currently at least two major programs underway in city towers in Sydney to achieve water reductions of that order.

The ‘3 Rs’ of water conservation are similar to those of waste management: reduce, replace, reuse. Waterless urinals, for example, avoid the need to flush 0.2L of urine with 9L of perfectly good drinking water, while new toilets reliably flush with 35 per cent less water than previously required. Flow controls can at least halve flows from taps and showers without a discernable loss of amenity values. Smart water metering and technologies for automatic leak detection and water cut off reduce consumption even further.

Starting with such a bottom up approach avoids waste in the first place and leaves us only to deal with the unavoidable rest. However, savings of up to 80 per cent could be obtained if the lightly polluted greywater from hand washbasins and showers was treated and reused on-site, complemented by rainwater harvesting. This should become the rule in any major refurbishment, and certainly for all new builds.

The new paradigm
Water saving technologies lead to a significant shift in the water balance for an office building. According to the Green Building Council of Australia’s Green Star building assessment tool, two-thirds of water use in a conventional office space – ignoring irrigation, cooling towers, food courts and the like – is equally divided between toilet and urinal flushing. The final third is used for hand washing, showers, in kitchens, for cleaning and lost through leaks.

In comparison, toilet flushing in a modern building with the latest technologies accounts for almost half the total water need, with taps and showers using about 21 per cent each. These two greywater streams combined almost equal the needs for toilet flushing.
Since use of the amenity taps is intrinsically linked to toilet use, with very little ‘pollution’ (a bit of soap), feeding this water to toilet cisterns makes a lot of sense. Treatment to meet stringent health authority standards is only minimal and a number of commercial package type plants are readily available.

All that is required is collection of this ‘waste’ as a resource in a separate stack, with only a small buffer. It ensures compliance with most authorities’ stipulations to not store greywater for more than 24 hours.

However, a significant challenge still remains in obtaining approval for the operation of such systems. There is still a long way to go to strike the right balance between protecting public health and appropriately relaxed requirements.

Real life operating data shows an integrated water conservation approach incorporating some simple internal recycling can feasibly reduce potable water use by 80 per cent in new or retrofitted office buildings. The challenge remains how to achieve such significant savings from existing building stock.

The answer lies in black water recycling and local cluster type recycling schemes, ranging from collecting easy-to-treat wastewater streams like greywater to rainwater and stormwater harvesting. Engineering such solutions will go a long way towards solving the water and sewage challenge of the 21st century.

Guenter Hauber-Davidson is MD of Water Conservation Group. Contact at ghd@watergroup.com.au