Q: Regarding the treatment of black water, grey water and rainwater harvesting, should I go all out when implementing water conservation methods in residential houses — is it worth the cost? What is the most efficient method of the three mentioned that would work well in more cost sensitive jobs? Are there any grounds for advising clients that they use their treated water for drinking even though legislation does not allow it?
A: Going all out is clearly a courageous thing to do, and without people doing such things throughout history, we would probably still be living in caves. Governments and regulators do not always see things this way, however, and such courage may be well and truly tested before it gets its way.
There is a strong argument for not having a multitude of micro-treatment systems scattered through the burbs when there is a functioning, centralised system that could provide total water reclamation. But the pioneers — the brave souls who attempt to change the world — prove to the dullard authorities both what is technically feasible and that people are not scared of such things. For this reason, if for no other, it is important that you seriously consider going all out. But consider also the cost benefit, because unless your project has a large benevolent budget, you may be best served by specifying a ‘less than all out’ system.
There are technically feasible systems that can treat black water to sufficient standards for flushing toilets or laundry use, but regulations vary around the nation as to its allowable reuse. In NSW, for instance, it can only be used inside commercial and multi- residential buildings. The authority’s assumption is that these buildings have managers whose job it is to ensure such systems are maintained, whereas single home owners may not.
To take water treatment to the next level — a truly potable standard — at the single domestic scale is probably not cost effective. But if Toowoomba could have done it on a city scale, all cities can. It is a lot less costly than desalination. It also happens in Germany and many other countries.
The most cost effective water efficiency strategy is to follow the tried and tested three-step rule:
1. Reduce demand by making the building as water efficient as possible. This includes selecting best available WELS rated taps and keeping the building small and wet areas close together.
2. Harvest available rainwater. Use this rule of thumb: maximise roof area collected, maximise tank volume and maximise use of the collected water, keeping in mind recycling options.
3. Recycle water to the extent allowed by local regulation and use for the maximum allowable under local regulations.
Note that this order is only true in a cost effective analysis. If you look at what is materially or resource effective, recycling always comes out ahead of harvesting. But efficiency of use is always on top.
Dick Clarke is principal of Envirotecture, which provides design and consulting services. He is an accredited building designer with 30 years experience, focusing exclusively on ecologically sustainable and culturally appropriate buildings. Clarke is director of sustainability and past president of the Building Designers Association of NSW.
