### Climate change

The quoted energy usage for early model reverse osmosis desalination plants is around 6 Watt-hours/litre. More modern plants appear to be more efficient and the quoted figures for WA and Vic are 4.1 and 4.6 respectively. A kilolitre of water costs around \$1.

Assuming a modern shower head using 9 litres/minute and a 5 minute shower, the energy cost of a 45 litre shower using desalinated water is around 200-250 Watt hours. [In Vic that is about 240-300 gm CO2.]

But think for a moment about the cost of heating the water. Most people shower in water at around 43 degrees C, which is around 30 degrees above the temperature of cold water. It costs 4200 Joules to heat 1 litre of water by
1 degree C and 1 Watt hour is 3600 Joules. Putting the numbers together you get 45 * 30 * 4200 / 3600 = 1575 Watt hours (1800 gm CO2). Boiling water is around 3 times the energy cost.

So before you complain too loudly about the cost of desalination, remember that heating water for your shower costs roughly 6 times as much energy as desalinating the water.

How much energy do you use? Do you have any idea?

Here in Melbourne we have been subjected to an unrelenting campaign of messages and restrictions aimed at reducing speeding and drink driving. No-one can have missed the message, and anyone who gets caught must not have been paying attention. Anyone driving here will know it works.

Likewise there has been a campaign of rules and announcements aimed at making us conscious of our water usage and reducing how much we use. This is personal consumption, where you get to turn off the tap. Everyone now knows that the target is 155 litres per person per day. It works: usage has dropped.

If anything energy usage and conservation is even more important, but does anyone know how much energy they use or how much they should be using? There is little doubt that a similar public awareness campaign could achieve similar results to reduce the the energy we have direct and personal control over as a consumer: the energy each of us could use less of by our own direct actions.
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The events in Copenhagen have made me do some thinking about what individuals are going to have to do to have an impact on climate change. I can identify roughly 4 broad categories.
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