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Will it cost me more to harvest rainwater?

Posted by Barry Nutley on 26 October 2009 at 2:32 pm

Rainwater harvesting systems tend to be pumped, causing people to ask the following questions :

1. "Does the cost of running the pump negate any savings made?"

2. "By running a pump, are we increasing our carbon emissions, and negating any environmental benefits?"

Well, to answer those questions:

1. It typically takes 1.5- 2.0 kWh to pump 1 cubic meter of water (1,000 litres). For a typical house using rainwater for WCs, washing machine and the garden, pumping costs are between 5-10p per week. To put that into context, the supply and waste water charges associated with 1 cubic metre are in the region of £2.50. A net gain of around £2.40 per cubic metre.

2). It takes around 5kWh of electricity to supply 1 cubic metre of water (this of course is used by your water authority), but harvested rainwater uses around 0.5kwh per cubic metre.

So, in essence, it is both financially and environmentally beneficial to install rainwater harvesting.

Photo by Photos8.com

About the author: Barry Nutley is co-founder and director of Viridis Energie Consultants

About the author: Barry Nutley is co-founder and director of Viridis Energie Consultants

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

1 comments - read them below or add one

Ian Smith

Ian SmithComment left on: 16 December 2009 at 3:59 pm

Consideration of whether a particular technology is environmentally beneficial should include embodied carbon in a life cycle assessment.  Judith Thornton wrote an article for GreenBuilding Magazine in the Spring 2008 edition which concluded that rainwater harvesting is worse than mains water supply when this factor was included.  There maybe water scarcity or flooding mitigation reasons for adopting it but saving carbon emissions does not seem to be a justifiable reason.

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