Pragma,

How much does it cost to construct 2 m deep reservoir of say 15 x 10? That's 300 kilolitres, so it would have to be filled from storm water captured from a significant area - the house roof is not big enough. What is the cost of the pipework required to do that, the pumps, and the electricity cabling to power the pumps?

It's no good saying that it will supply a family of four for ten months. What happens afterwards, in a drought? Or to put it another way, what are the additional costs required to ensure that the water never runs out?

So far you're not providing costings, you're just offering points that you think represent an argument that it must be cheaper than desalination. If it is cheaper, then provide the analysis that proves it.

silvia, sure, building reservoirs would incur more expenses than not building any. but once built that's it. look at how much it cost to build warragamba and other dams. the running costs are a fraction in comparison. a huge desal plant however, would cost a fortune to construct and a fortune to run. can you imagine how much water rates would be if it had to be produced by machinery with ongoing costs ? that is a clear enough analysis. the average annual sydney rainfall is 1000mm. that's 150 kl for our house reservoir. it's also a hell of a lot of water that doesn't need to be supplied. of course larger buildings would yield more water. imagine all the grey water that could be stored for irrigation. the practical solutions are many. the problem with practical water solutions is that many consultants would miss out on syphoning the money reservoirs..
the real issue is not so much one of value for money. it's value vs money. the real value is in having an athmosphere and environment that won't need environmentally friendly power plants to make more athmosphere because we're ruining it by running power plants to make more water. that is also a clear analysis. if you really need a $ analysis then just get quotes.

Pragma,

We already know the cost impacts of a desalinator. The costings have been done, and Perth has almost finished building one. In Sydney, supplying *all* the water by desalination would cost about 50cents per kilolitre more than the current supply. In the face of that, hand waving arguments about capital and running costs are meaningless.

If your position is that storm water collection would be cheaper, then the onus is really on you to show that, and so far you've not done anything in that direction.

As for "silvia, sure, building reservoirs would incur more expenses than not building any. but once built that's it."

No, that's not it, by a long shot. Look at the thread entitled "The bane of my life: discounted cash flow."

Sylvia.

50 cents a kl is cheap. ours cost 5 cents a litre. what acreage will the proposed sydney plant require including the storage facilities. (i'll google the perth stats) with the many megalitre/day production what size are the proposed cleaning reject water reservoirs. how are they going to dispose of the water/chemical cocktail. with that kind of production i can't envisage evaporation being able to keep up with it. how are they going to prevent it from seeping into the aquifer. how will birdlife be prevented from consuming this water. what plans are there for the disposal of so many used membranes. can you recommend a www. site that has these explanations.
my concern is, how will we know when we reach critical point with overloading the environment with chemicals and emission. i doubt if nature will give us a sign along the lines of "ok people, you're getting close to to the limit, turn back now". it will be "sorry mankind, you've done your dash". science has provided us with many fantastic remedies so far but how many preventions can be listed.

It's not 50cents/kL, it's an additional 50 cents/kL on top of what the Sydney Catchment Authority gets paid for its water.

There's some discussion of the proposed Sydney desalinator here:

http://www.waterforlife.nsw.gov.au/__data/assets/pdf_file/1459/06mwp_chapter_7.pdf