Tapping the oceans

economist.com

5 points·0_o··5 comments

Desalination has been around for quite some time, but the alternatives are so much less expensive that it's adoption won't increase until populations reach critical levels.

Maybe we have reached a critical point of potable water shortage because according to the this report http://www.bccresearch.com/report/MST052A.html,

"The global market for seawater and brackish water desalination plants increased from $1.7 billion in 2005 to $1.9 billion in 2007. It should reach $3.6 billion by 2012, a compound annual growth rate (CAGR) of 13.4%."

Hold up $1.7 billion in 2005 to $1.9 billion in 2007 is not 13.4%. 1.9billion/1.7billion = 1.118 but it's over 2 years so: 1.118 ^.5 = 1.057 which is ~2% faster than inflation.

Edit: 1.7billion * 1.7 * 1.057 * 1.057 = 1.9billion and 1.9 billion * 1.057 ^5 is 2.5billion in 2012. So, their numbers seem off.

They calculated the compound annual growth rate

CAGR = ((last number/firs tnumber)^(1/number of years))-1

The assumption is that the first year is 1.7 billion, last year is 3.6 billion and the number of years are 6, as they appear to assume that "by 2012" means 2012 is not included as a year in the calculation, giving a 7 year span. But they also excluded 2005 to give a 6 year span.

so the calculation is ((3.6 / 1.7) ^ (1/6)) -1 = 13.2%.

Still, they are off by 0.2% if you keep to 2 significant digits in the calculations and not use selective rounding. And they did fudge the span of years, making (intentional or not) the growth look better.

> The Perth plant, which uses technology from Energy Recovery, a firm based in California, consumes only 3.7kWh to produce one cubic metre of drinking water.

This comes out to $0.37/264gal of water, assuming $0.10/kWh.

edit: should have read the next paragraph before posting :-/

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