News from the CEPA e-mail list

Rainwater harvesting and more on solar distillers (24/07/07)

Dear List members:

Thanks to list members for the interesting discussion on rainwater harvesting that has naturally followed on from Terry's comment on solar distillers a few days ago. Some time ago I met some people from the Rainwater Harvesting Alliance, which has its Secretariat based here in Geneva. It's a global alliance engaged in lobbying and advocacy to position rainwater harvesting in development agendas. There is a good information on their web site http://www.irha-h2o.org to show rainwater harvesting success stories with their current news covering projects in France, Canada, Uganda, the Gambia, Japan and more. I have also in the past been on this web site http://www.rainwaterharvesting.org which has been set up specifically for rainwater harvesting information for India by the Centre for Science and Environment, a New Delhi based NGO. A wealth of information on rainwater harvesting know-how to be found here.

I did follow up with Terry on the broader utility of the solar distillers he wrote about and he has helpfully noted that "More than 90% of the water fed is recovered. The remaining balance is trace, but still, we can recycle further by feeding it to some salt tolerant local plant species, say to mangroves, it will absorb these excess salts and convert into biomass (ideal if the feed water is saline or brackish, also called "phytoremediation"). If the residue is Arsenic or Iron, it can be also made immovable by mixing with clay and converting into bricks. Residue disposal is not a major issue, as far as our experimentations prove.

Solar desalination is a de- centralized potable water making option, suited for developing countries 30 degrees North and South latitude of the Equator. These solar desalination panels can be very made or placed over roofing similar to any other solar devices. Further research is still warranted to produce more water per unit size solar still. Our first model was giving 1 liter per sq. meter per day, but now we get about 5 liters per sq.m per day. We are now designing a model that should yield 10 liters per sq.m. per day, a dream today. All these experimentations are carried out in wetlands and coastal areas." I'm sure Terry would be happy to give more detailed information if you send him an email at tthomas@eth.net.

Just to be sure that we don’t feel too negative towards the WWF report I reviewed, I did check what they had to say about solar distillers. For example, they say “Low energy, low technology thermal distillation is possible using energy sources such as the sun (solar distillation), but the area required for large scale water production is generally prohibitive and facilities remote from their markets can lose any energy savings in pumping costs. However, small scale solar distillation can augment the water supplies of small communities and has been successfully trialled in Botswana.” This fits well with the experiences Terry has shared and it would be interesting to know just how much this is being used in different parts of the world suited to this low-tech approach - I would encourage Terry to contact the author and pass on his experiences.

All for now, Sandra Hails, Ramsar Secretariat

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