Such vague claims contribute little to the debate, and can seriously derail it.

well, in theory the kilowatt figures appear reasonable but in reality, the scenario does change. by increasing water availability EVERYTHING else increases as well. more water=more industry=more polution and that's not a theory. on top of that sylvia are you aware of how much concentrated bacteria laden reject water is going back into the ocean ? two thirds of water going through the membranes are reject. have you any inkling what this does to the marine life and coastal vegetation ? google it if you don't think i have no idea. i work in that industry. desalination is a short term solution and only acceptable on a small scale. machinery requires constant upgrading and servicing which always involves poluting agents.
a dam on the other hand is far less maintenance intensive and even provides much needed good recreational value. imagine, the hard thinking theorists could even go for a swim and cool their hot heads.

Pragma,

I take you're annoyed that I've undermined your argument that desalination is too energy intensive. So now you've decided to raise other issues, but again without providing any concrete data.

Regarding the alleged bacterial problem, desalination doesn't increase the number of bacteria, just their concentration, It also increases the salinity, which some of the bacteria will no doubt not survive. Anyway, bacteria are not an inherently bad thing. They are part of the food chain.

I don't doubt that the more concentrated salty water has an effect in the immediate area where it's released, but it's not as if dams are innocuous in that respect, because they destroy habitat for land animals and plants. In any case, there are limited options for building new dams. You can't just build one anywhere.

The fact that desalination plants require maintenance is just a cost of production. A plant has a definite life after which it needs to be scrapped and rebuilt. This is also just a cost of production.

You have not provided any evidence that the maintenance necessarily involves pollution.

sylvia i appreciate your reply. desal membranes require periodic (3mths min. dep. on raw water quality) chemical cleaning with alkaline and acid cleaners at a rate of 20/100. the pumps require substantial oil changes ie. a 50 tonne/day, 30 kw high pressure pump has an oil capacity of 8 litres. it goes without saying the bigger the pump the more oil. the primary and secondary filters also require frequent replacement although there is no apparent chemical pollution from discarded filters they still need to be manufactured. membranes have a very high failure rate in the manufacture process and that also is a substantial contributor to pollution. the internet as you are well aware, provides all the info you wish to find. i am by no means a raging greenie however, it is my view that the threat to our athmosphere is far less from a dam than from the emission of oil based machinery and so-called environmentally friendly technology distorts the grim reality of the high pollution rate from it's mainly oil-based manufacture.

btw no-one actually argues that dams have no impact. they just have less impact. whilst some wildlife habitat is obviously submerged it is not destroyed as such. wildlife is adaptable and relocating up the slopes is not without consequences. natural cycles do not revolve around wildlife. wildlife adapts and revolves around the cycles of nature as it does with much of human interference. the most important consideration for us to concentrate on is the minimising of the impact. we can not eliminate any impact unless we eliminate ourselves. step forward the hardened conservationists ! :-)

Pragma, wildlife includes much more than just the mobile fauna. What about all the plants?

“Whilst some wildlife habitat is obviously submerged it is not destroyed as such.”

The submerged habitat is destroyed. How can you argue otherwise?

“The most important consideration for us to concentrate on is the minimising of the impact.”

Absolutely. And this is why it is of vital importance to declare limits to the size of us. ie, the population… and hence the demand for water and all sorts of other resources.

The very fact that we are considering things like desalination plants means that we have grossly overstepped the point at which humanity should have stabilised its numbers in places like Perth and Sydney….. and yet we just keep on growing. Crazy stuff!

It is far from clear to me that a dam has less net impact on the environment than a desalinator of equivalent capacity if the CO2 aspects of the desalinator are eliminated by way of sustainable power generation.

There is not just the permanent flooding of the land, but a reduction in flows downstream of the dam. There is also an elimination of periodic temporary flooding downstream, and a cessation of passage of silt.

The silt also eventually fills the reservoir rendering it useless, so dams are not sustainable in the long term.

However, in the case of Sydney, the issue of whether dams are better or worse than desalinators is largely moot, because of the absence of suitable places to build new dams. The question is really whether Sydney residents would prefer to have a desalinator built, or endure the current level of water restrictions indefinitely, with the consequences such as the one I discussed at the start of this thread.

This should be a community decision based on facts. At the moment, the community has been fed half-truths and misinformation by people with a different agenda.