Like it not, we are going to have to do something about water use in Australia. With our dam capacity at all time lows and per capita consumption increasing, we are over consuming our most precious resource. A business as usual approach is not an option, and it is time to for action and there are many things we can do as Chartered Surveyors.
After the US and Canada, Australia has the highest per capita extraction of water in the world. Given that Canada has 75% of the world fresh water supply and Australia is the such a dry continent in the midst of an extended drought these are alarming statistics. So how much water do we use and how much do we need? Looking at household consumption as a benchmark we use water for cooking, bathing, washing, drinking, gardening, and toilet flushing. Minimum requirements per person per day are 60 litres, and a comfortable level is established at 125 litres per day however we typically consume in the region of 390-1450 litres per person per day here - these figures represent excessive over consumption by anyone’s standards (Crockett & Carroll, 1997). Not surprisingly since June 2006 Melbourne’s dam capacity has reduced from 47% to 28% in 12 months. In San Francisco authorities are already taking action over water conservation and their dams are at 72% capacity.
With the Commonwealth and State management of water resources in a state of disarray with ongoing negotiations relating to the Murray Darling system, there is no time to wait for a coherent policy led initiative and we need to take the lead in cutting water consumption in buildings as a matter of urgency. Always the first and best option is to reduce consumption per se, secondly direct recycling of water within buildings should be undertaken and thirdly recycling of water non a larger city wide scale should be adopted. Deslaination is the last resort as the plants are energy intensive, expensive and produce large quantities of saline which present an environmental issue in terms of safe disposal.
Case Study 1 - Mawson Lakes, Adelaide, SA.
This is a residential scheme on a Greenfield site which has been provided with a dual water supply. Located 12K north of Adelaide, Mawson Lakes will have approximately 11,000 residents in 4,300 homes by 2010, plus 6,000 students and a business community of 8,000. 70 hectares of lakes and waterways will be provided on the site with 189 hectares of open space representing 30% of the total area of Mawson Lakes.
The second water supply provides non potable recycled water for use in toilet flushing, gardening and car washing. The project started using the water in April 2005. The schematic (available for download in the right hand column) illustrates how the scheme operates.
Readers are recommended to view the web site, in the top right hand column, which has a series of information downloads which are extremely useful for surveyors.
Case Study 2 - CH2 Melbourne
This is an office development located in the CBD and completed in 2006. A US study found the majority of wastewater in offices is blackwater (around 40 kL/day out of a total waste flow of 45.4kL/day) therefore 90% of a building water usage need not be of a potable or drinking water standard. As a result the water saving technologies here include sewer or black water mining, with recycled water for toilet flushing, use in the cooling tower system, street tree and garden watering, the goals were to reduce consumption and reuse water where possible. The AAAA level fittings, i.e. showers with a flow rate of 9L/min, taps at 4L/min, toilets with a 4.5L flush and urinals with sensor triggered flushing will result in 30% water savings.
The schematic (Figure 1 - Water Cycle of CH2) available in the right hand download column shows a multi water reuse treatment. Around 95% of the contents of the sewer is water. With this system black water is drawn in and filtered with the solids returned to the sewer. The recovered water is then used in the building for non potable uses, although the water quality is good enough to drink, the owners felt that there are still issues to address regarding community acceptance. Cross contamination of the supplies is not possible as the water supplies are separated.
Another feature of water reuse is the rainwater capture from the roof of the building. With a roof area of 1500m², assuming 70% capture and a rainfall of around 55mm/month a yield of 57kL/month is expected and is used for toilet flushing, landscape watering and the cooling towers.
These two mini case studies have shown that substantial water savings are possible in different building types, using a range of low technologies and innovative technologies. With a widespread use and adoption of these technologies, surveyors can ensure our excessive water consumption starts to decline to a more sustainable level.
