Desalinated mouthwash!
"What is wrong with desalination? After all, it does not rely on rainfall,
is used by many places overseas, and is sustainable".
I have been asked this, or something similar, by a variety of people who see merit in providing a `permanent solution to Sydney?s water crisis`.
The Society`s position on desalination versus recycling, stormwater harvesting and rainwater tanks is presented on its website in a critical review of the Metropolitan Water Plan. It is comprehensive and well worth downloading. But the following specifically deals with the above question and beliefs.
We start with sustainability and rainfall dependency. The oceans provide a sustainable source of seawater because, being the world`s principal reservoir within the hydrologic cycle, there is negligible rainfall dependency. So surely this says we should use desalination? Well, I am afraid not, but to explain this, sustainability needs to consider the environmental cost.
For plants of equivalent capacity, the power costs for desalination vary from 3 to more than 6 times those of potable recycling. So, if this is translated into equivalent greenhouse gas emissions, desalination is a vastly bigger atmospheric polluter. The State Government says that it will offset the pollution by planting trees or perhaps through carbon trading. Fine, but the pollution will enter the atmosphere and hasten the build-up of greenhouse gases long before any tree-effect kicks in. And if carbon trading is employed, the cost of water from this power-hungry option will rise disproportionately. The conclusion must be that the power demands of desalination are neither environmentally nor economically sustainable.
A similar type of argument relates to the high capital costs of desalination plants compared with recycling plants of equivalent capacity. Because seawater is corrosive, more robust material-specifications are needed to achieve an equivalent plant life. This again translates into both higher greenhouse gas emissions and water prices thereby detracting from desalination`s environmental and economic sustainability.
OK, if desalination produces high-price water (compared with recycling and stormwater harvesting) and is environmentally unsustainable, why do many places use it? There is a range of answers. Some say their systems were in place before climate change impacts were fully appreciated (the `hindsight` excuse). Others have cheap and non-polluting hydroelectric power or geothermal power (e.g. Iceland or New Zealand), or have negligible rainfall to compensate for recycling losses and are blessed with cheap oil-based power (e.g. certain middle eastern countries), or have subsidised fuel-oil costs (e.g. small communities in Greenland); and many disregard the unsustainable environmental consequences and are effectively in denial. For those still `planning` (e.g. Perth and Sydney), there is no justification for desalination, despite it supposedly being an insurance policy `should normal rainfall fail`, because their choice will hasten the climate change that links with declining rainfall. Desalination is an environmentally and economically unsustainable way of producing high-price water.
Allowing all this, what else is wrong with desalination? Well, for completeness, it is far less amenable than potable recycling to stormwater harvesting, and it reinforces the wasteful `single pass` (use it once and throw it away) approach to water resources. Even if not/little used, as the State Government would have us believe, maintenance costs still accrue and a $1.3 to 1.9 billion capital cost is a very expensive insurance policy!
Brian Marshall,
Groundwater Subcommittee.