Interesting tidbit from the Land Down Under:
Quote
Rainwater tanks can save a lot of water, but preliminary Australian research warns pumping water from them can be energy intensive.
We should ensure we don't create an energy problem while trying to solve a water problem, says Professor Stuart White of the Institute for Sustainable Futures at the University of Technology in Sydney.
[..]
He says Australia has the widest application of rainwater tanks in the world, especially in urban areas, encouraged by government rebates.
White says gravity is a useful way to deliver rainwater to taps, but it is not always feasible in urban areas because tanks need to be higher than the roof to provide sufficient pressure for showers.
As a result most households use small pumps that switch on every time you turn the tap on, even if it's just briefly to clean your teeth or flush the toilet.
"It means you have a pump running at full revs to do a tiny amount of work," says White.
[..]
In what is believed to be the first study of its kind, White and colleagues, monitored the rainwater consumption and associated energy consumption of 8 households in Sydney and Newcastle.
They calculated the "energy intensity" of household rainwater systems, which is the amount of energy used to get each kilolitre of water to the tap.
They found in most cases pumping water from rainwater tanks is more energy intensive than getting it from mains water, although lower than getting it from desalination.
White says the standard suburban system rainwater tank with pump had an energy intensity of 1.5 kilowatt-hours per kilolitre.
"The water that you get out of a tap would be less than 1 [kilowatt-hour per kilolitre]," he says.
Source: http://www.abc.net.au/news/stories/2009/05/27/2582450.htm?section=justin (http://www.abc.net.au/news/stories/2009/05/27/2582450.htm?section=justin)
Collecting rainwater seems like you're getting something for nothing, eh? But no, now you're paying for electricity to run a pump to create pressure in the line so you can actually have a shower...